Analyte sensors and sensing methods featuring dual detection of glucose and ketones

ABSTRACT

Glucose and ketones may be dysregulated singularly or concurrently in certain physiological conditions and may be advantageously assayed together using an analyte sensor capable of detecting both analytes. Certain analyte sensors capable of dual detection may comprise a first working electrode and a second working electrode, a ketones-responsive active area disposed upon a surface of the first working electrode, a glucose-responsive active area comprising a glucose-responsive enzyme disposed upon a surface of the second working electrode, a membrane having a first portion overcoating the ketones-responsive active area and a second portion overcoating the glucose-responsive active area, in which the first portion and the second portion have different compositions. The ketones-responsive active area comprises an enzyme system comprising at least two enzymes that are capable of acting in concert to facilitate detection of ketones.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority of U.S.Provisional Application 62/797,566 entitled “Analyte Sensors EmployingMultiple Enzymes and Methods Associated Therewith,” filed on Jan. 28,2019, and U.S. Provisional Application 62/884,869 entitled “AnalyteSensors and Sensing Methods Featuring Dual Detection of Glucose andKetones,” filed on Aug. 9, 2019, the entireties of which is incorporatedherein by reference.

BACKGROUND

The detection of various analytes within an individual can sometimes bevital for monitoring the condition of their health and well-being.Deviation from normal analyte levels can often be indicative of anunderlying physiological condition, such as a metabolic condition orillness, or exposure to particular environmental conditions. While asingle analyte may be singularly dysregulated for a given physiologicalcondition, it is sometimes the case that more than one analyte isconcurrently dysregulated, either due to the same physiologicalcondition or resulting from a comorbid (related) physiologicalcondition. When multiple analytes are concurrently dysregulated, theextent of dysregulation may vary for each analyte. As such, each analytemay need to be monitored to obtain a satisfactory evaluation of anindividual's health.

Periodic, ex vivo analyte monitoring using a withdrawn bodily fluid canbe sufficient to observe a given physiological condition for manyindividuals. However, ex vivo analyte monitoring may be inconvenient orpainful for some persons, particularly if bodily fluid withdrawal needsto occur fairly frequently (e.g., several times per day). Continuousanalyte monitoring using an implanted in vivo analyte sensor may be amore desirable approach for individuals having severe analytedysregulation and/or rapidly fluctuating analyte levels, although it canalso be beneficial for other individuals as well due to the convenienceoffered. Subcutaneous, interstitial, or dermal analyte sensors canprovide sufficient measurement accuracy in many cases while affordingminimal user discomfort.

Many analytes represent intriguing targets for physiological analyses,provided that a suitable detection chemistry can be identified. To thisend, amperometric sensors configured for assaying glucose in vivo havebeen developed and refined over recent years to aid in monitoring thehealth of diabetic individuals. Other analytes commonly subject toconcurrent dysregulation with glucose in diabetic individuals include,for example, lactate, oxygen, pH, A1c, ketones, and the like. Sensorsconfigured for detecting analytes commonly dysregulated in combinationwith glucose are known but are considerably less refined at present.

In vivo analyte sensors typically are configured to analyze for a singleanalyte in order to provide specific analyses, oftentimes employing anenzyme to provide high specificity for a given analyte. Because of suchanalytical specificity, current in vivo analyte sensors configured forassaying glucose are generally ineffective for assaying other analytesthat are frequently dysregulated in combination with glucose orresulting from dysregulated glucose levels. At best, current analytemonitoring approaches require a diabetic individual to wear twodifferent in vivo analyte sensors, one configured for assaying glucoseand the other configured for assaying another analyte of interest, suchas lactate or ketones. Analyte monitoring approaches employing multiplein vivo analyte sensors may be highly inconvenient for a user. Moreover,when multiple in vivo analyte sensors are used, there is an added costburden for equipment and an increased statistical likelihood for failureof at least one of the individual in vivo analyte sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are included to illustrate certain aspects of thepresent disclosure, and should not be viewed as exclusive embodiments.The subject matter disclosed is capable of considerable modifications,alterations, combinations, and equivalents in form and function, withoutdeparting from the scope of this disclosure.

FIG. 1 shows a diagram of an illustrative sensing system that mayincorporate an analyte sensor of the present disclosure.

FIGS. 2A-2C show diagrams of particular enzyme systems that may be usedfor detecting ketones according to the disclosure herein.

FIGS. 3A-3C show cross-sectional diagrams of analyte sensors having aglucose-responsive active area and a ketones-responsive active area upona single working electrode.

FIG. 4 shows a cross-section diagram of an analyte sensor having aglucose-responsive active area and a ketones-responsive active area uponseparate working electrodes.

FIGS. 5A-5D show perspective views of analyte sensors featuringsubstantially cylindrical electrodes that are disposed concentricallywith respect to one another.

FIG. 6 shows four replicates of the response for an electrode containingdiaphorase, NAD⁺, and β-hydroxybutyrate dehydrogenase when exposed tovarying β-hydroxybutyrate concentrations.

FIG. 7 shows an illustrative plot of average current response versusβ-hydroxybutyrate concentration for the electrodes of FIG. 6 .

FIG. 8 shows an illustrative plot of current response for the electrodesof FIG. 6 when exposed to 8 mM of β-hydroxybutyrate in 100 mM PBS at 33°C. for 2 weeks.

FIG. 9 shows an illustrative plot of the response for an analyte sensorcontaining a glucose-responsive active area and a ketones-responsiveactive area disposed upon separate working electrodes following exposureto 30 mM glucose and 10 mM ketones.

FIGS. 10-12 show illustrative plots of the response of an analyte sensorcontaining a glucose-responsive active area and a ketones-responsiveactive area to varying concentrations of glucose and β-hydroxybutyrate.

FIGS. 13A and 13B show four replicates of the response for an electrodecontaining NADHOx, NAD⁺, and β-hydroxybutyrate dehydrogenase whenexposed to varying β-hydroxybutyrate concentrations.

FIG. 14 shows an illustrative plot of current response versus time foran electrode containing NADHOx, NAD⁺, and β-hydroxybutyratedehydrogenase after exposure to increasing β-hydroxybutyratedehydrogenase concentrations.

FIG. 15A shows the current response for a carbon working electrode, andFIG. 15B shows the current response for a carbon nanotube workingelectrode, each containing poly-1,10-phenanthroline-5,6-dione andβ-hydroxybutyrate dehydrogenase.

FIG. 16 is a schematic diagram of an example analyte monitoring andvehicle control system, according to one or more embodiments of thepresent disclosure.

DETAILED DESCRIPTION

The present disclosure generally describes analyte sensors employingmultiple enzymes for detection of two different analytes and, morespecifically, analyte sensors employing multiple enzymes for detectionof glucose and ketones and corresponding methods for use thereof.

As discussed above, analyte sensors employing an enzyme are commonlyused to detect a single analyte, such as glucose or a related analyte,due to the enzyme's frequent specificity for a particular substrate orclass of substrate. However, the monitoring of multiple analytes may becomplicated by the need to employ a corresponding number of analytesensors to facilitate the separate detection of each analyte. Thisapproach may be problematic or undesirable, especially when monitoringmultiple analytes in vivo, due to issues such as, for example, the costof multiple analyte sensors, user discomfort when wearing multipleanalyte sensors, and an increased statistical likelihood for failure ofan individual analyte sensor.

The present disclosure provides analyte sensors that are responsive toboth glucose and ketones, two analytes that are commonly dysregulated indiabetic individuals. Since glucose and ketones concentrations may notdirectly correlate with each other in a diabetic individual alsoexhibiting ketoacidosis (ketone dysregulation), it may be advantageousto monitor both analytes concurrently using the analyte sensorsdisclosed herein, potentially leading to improved health outcomes. Inaddition to providing health benefits for diabetic individuals, theanalyte sensors may be beneficial for other individuals who wish tomonitor their ketones levels, such as individuals practicing a ketogenicdiet. Ketogenic diets may be beneficial for promoting weight loss aswell as helping epileptic individuals manage their condition. Concurrentglucose monitoring during ketogenic diet monitoring may offer relatedadvantages.

In particular, the present disclosure provides analyte sensors in whicha glucose-responsive active area and a ketones-responsive active areaare present within the tail of a single analyte sensor, thereby allowingboth analytes to be monitored concurrently for identifying potentialdysregulation thereof using the single analyte sensor. As evident fromthe description above, the concurrent detection of glucose and ketonesusing a single analyte sensor may provide several advantages overmonitoring approaches employing separate analyte sensors. Variousphysical dispositions of the glucose-responsive active area and theketones-responsive active area are possible within the analyte sensors,as discussed hereinafter. Particular implementations of the presentdisclosure include sensor architectures in which the glucose-responsiveactive area and the ketones-responsive active area may be interrogatedseparately to determine the concentration of each analyte, such asthrough disposing the active areas upon separate working electrodes. Asdiscussed hereinafter, there are challenges associated withincorporating active areas featuring different detection chemistriesupon a single analyte sensor, which are addressed by the presentdisclosure.

Glucose-responsive analyte sensors are a well-studied and stilldeveloping field to aid diabetic individuals in better managing theirhealth. Despite the prevalence of comorbid analyte dysregulation indiabetic individuals, sensor chemistries suitable for detecting ketonesand other analytes commonly dysregulated in combination with glucosehave significantly lagged behind the more well-developed glucosedetection chemistries. The present disclosure alleviates this deficiencyby providing sensor chemistries suitable for detecting ketones with goodresponse stability over a range of ketones concentrations, particularlydetection chemistries utilizing enzyme systems comprising at least twoenzymes that are capable of acting in concert to facilitate detection ofketones. As used herein, the term “in concert” refers to a coupledenzymatic reaction, in which the product of a first enzymatic reactionbecomes the substrate for a second enzymatic reaction, and the secondenzymatic reaction serves as the basis for measuring the concentrationof the substrate (analyte) reacted during the first enzymatic reaction.Although defined in terms of two coupled enzymatic reactions, it is tobe appreciated that more than two enzymatic reactions may be coupled aswell in some instances. For example, the product of a first enzymaticreaction may become the substrate of a second enzymatic reaction, andthe product of the second enzymatic reaction may become the substratefor a third enzymatic reaction, with the third enzymatic reactionserving as the basis for measuring the concentration of the substrate(analyte) reacted during the first enzymatic reaction. Discussion ofsuitable enzyme systems for detecting ketones according to thedisclosure herein follows hereinbelow.

It may be desirable to utilize two or more enzymes acting in concertwith one another to detect a given analyte of interest when a singleenzyme is unable to facilitate detection. Situations in which a singleenzyme may be ineffective for promoting analyte detection include, forexample, those in which the enzyme is inhibited by one or more productsof the enzymatic reaction or is unable to cycle between an oxidizedstate and reduced state when disposed within an analyte sensor. Someproducts produced by a single enzyme may not be electrochemicallydetectable.

Even having suitable detection chemistries in hand, combining aglucose-responsive active area and a ketones-responsive active area upona single analyte sensor is not a straightforward matter.Glucose-responsive analyte sensors commonly employ a membraneovercoating the glucose-responsive active area to function as a masstransport limiting membrane and/or to improve biocompatibility. Limitingglucose access to the glucose-responsive active area with a masstransport limiting membrane can aid in avoiding sensor overload(saturation), thereby improving detection performance and accuracy. Amass transport limiting membrane may act as a diffusion-limiting barrierto reduce the rate of mass transport of glucose to accomplish theforegoing. The mass transport limiting membrane may be homogeneous andcomprise a single membrane polymer in conventional glucose-responsivesensors. Unfortunately, glucose and ketones exhibit significantlydifferent permeability values through a given membrane material, suchthat if a single mass transport limiting membrane overcoats the activeareas of an analyte sensor capable of detecting both glucose andketones, significantly different sensitivities may be realized for eachanalyte, thereby complicating one's ability to detect glucose andketones concurrently and accurately. Although analyte sensitivity issuesmay be addressed, in principle, by adjusting the membrane thicknessand/or altering the size of the active areas with respect to oneanother, these solutions may be difficult to implement in practice.

In response to the foregoing, the present disclosure also providesmembrane compositions and methods for deposition thereof that aresuitable to facilitate concurrent detection of glucose and ketones.Specifically, the present disclosure provides membrane compositionshaving different permeability values that may be disposed separately asdistinct compositions upon the glucose-responsive active area and theketones-responsive active area. Surprisingly, a membrane polymersuitable for use as a mass transport limiting membrane in aglucose-responsive analyte sensor may also be suitably incorporated in amulti-component mass transport limiting membrane for overcoating theactive area in a ketones-responsive analyte sensor, even when themembrane polymer alone is otherwise unsuitable for use with ketones dueto poor performance (e.g., undesired permeability values).Advantageously, the architectures of the analyte sensors disclosedherein allow a continuous membrane having a homogenous membrane portionto be disposed upon the glucose-responsive active area of the analytesensors and a multi-component membrane portion to be disposed upon theketones-responsive active area of the analyte sensors, therebylevelizing the permeabilities of each analyte concurrently to affordimproved sensitivity and detection accuracy. As used herein, the term“homogenous membrane” refers to a membrane comprising a single type ofmembrane polymer, and the term “multi-component membrane” refers to amembrane comprising two or more types of membrane polymers. Both bilayerand admixed membranes may be suitable for use as the multi-componentmembrane in the disclosure herein. By utilizing a multi-componentmembrane in conjunction with the sensor architectures disclosed herein,manufacturing advantages may be realized when combiningglucose-responsive and ketones-responsive detection chemistries with oneanother, as compared to manufacturing approaches that alter the membranethickness and/or the size of the active areas for adjusting thesensitivity of one of the analytes.

Before describing the analyte sensors of the present disclosure infurther detail, a brief overview of suitable in vivo analyte sensorconfigurations and sensor systems employing the analyte sensors will beprovided first so that the embodiments of the present disclosure may bebetter understood. FIG. 1 shows a diagram of an illustrative sensingsystem that may incorporate an analyte sensor of the present disclosure,specifically an analyte sensor comprising a glucose-responsive activearea and a ketones-responsive active area. As shown, sensing system 100includes sensor control device 102 and reader device 120 that areconfigured to communicate with one another over a local communicationpath or link, which may be wired or wireless, uni- or bi-directional,and encrypted or non-encrypted. Reader device 120 may constitute anoutput medium for viewing analyte concentrations and alerts ornotifications determined by sensor 104 or a processor associatedtherewith, as well as allowing for one or more user inputs, according tosome embodiments. Reader device 120 may be a multi-purpose smartphone ora dedicated electronic reader instrument. While only one reader device120 is shown, multiple reader devices 120 may be present in certaininstances. Reader device 120 may also be in communication with remoteterminal 170 and/or trusted computer system 180 via communicationpath(s)/link(s) 141 and/or 142, respectively, which also may be wired orwireless, uni- or bi-directional, and encrypted or non-encrypted. Readerdevice 120 may also or alternately be in communication with network 150(e.g., a mobile telephone network, the internet, or a cloud server) viacommunication path/link 151. Network 150 may be further communicativelycoupled to remote terminal 170 via communication path/link 152 and/ortrusted computer system 180 via communication path/link 153.Alternately, sensor 104 may communicate directly with remote terminal170 and/or trusted computer system 180 without an intervening readerdevice 120 being present. For example, sensor 104 may communicate withremote terminal 170 and/or trusted computer system 180 through a directcommunication link to network 150, according to some embodiments, asdescribed in U.S. Patent Application Publication 2011/0213225 andincorporated herein by reference in its entirety. Any suitableelectronic communication protocol may be used for each of thecommunication paths or links, such as near field communication (NFC),radio frequency identification (RFID), BLUETOOTH® or BLUETOOTH® LowEnergy protocols, WiFi, or the like. Remote terminal 170 and/or trustedcomputer system 180 may be accessible, according to some embodiments, byindividuals other than a primary user who have an interest in the user'sanalyte levels. Reader device 120 may comprise display 122 and optionalinput component 121. Display 122 may comprise a touch-screen interface,according to some embodiments.

Sensor control device 102 includes sensor housing 103, which may housecircuitry and a power source for operating sensor 104. Optionally, thepower source and/or active circuitry may be omitted. A processor (notshown) may be communicatively coupled to sensor 104, with the processorbeing physically located within sensor housing 103 or reader device 120.Sensor 104 protrudes from the underside of sensor housing 103 andextends through adhesive layer 105, which is adapted for adhering sensorhousing 103 to a tissue surface, such as skin, according to someembodiments.

Sensor 104 is adapted to be at least partially inserted into a tissue ofinterest, such as within the dermal or subcutaneous layer of the skin.Sensor 104 may comprise a sensor tail of sufficient length for insertionto a desired depth in a given tissue. The sensor tail may comprise atleast one working electrode and a glucose-responsive active area and aketones-responsive active area upon a surface of the at least oneworking electrode to facilitate detection of these analytes. A counterelectrode may be present in combination with the at least one workingelectrode. Particular electrode configurations upon the sensor tail aredescribed in more detail below in reference to FIGS. 3A-5D.

One or more mass transport limiting membranes may overcoat theglucose-responsive active area and the ketones-responsive active areaupon the at least one working electrode, as also described in furtherdetail below. The glucose-responsive active area may comprise aglucose-responsive enzyme and the ketones-responsive active area maycomprise an enzyme system comprising at least two enzymes that arecapable of acting in concert to facilitate detection of ketones.Suitable enzyme systems are further described below in reference toFIGS. 2A-2C. The glucose-responsive active area and theketones-responsive active area may each include a polymer to which atleast some of the enzymes are covalently bonded, according to variousembodiments. In various embodiments of the present disclosure, glucoseand ketones may be monitored in any biological fluid of interest such asdermal fluid, interstitial fluid, plasma, blood, lymph, synovial fluid,cerebrospinal fluid, saliva, bronchoalveolar lavage, amniotic fluid, orthe like. In particular embodiments, analyte sensors of the presentdisclosure may be adapted for assaying dermal fluid or interstitialfluid to determine concentrations of glucose and/or ketones in vivo.

Referring still to FIG. 1 , sensor 104 may automatically forward data toreader device 120. For example, analyte concentration data (i.e.,glucose and/or ketones concentrations) may be communicated automaticallyand periodically, such as at a certain frequency as data is obtained orafter a certain time period has passed, with the data being stored in amemory until transmittal (e.g., every minute, five minutes, or otherpredetermined time period). In other embodiments, sensor 104 maycommunicate with reader device 120 in a non-automatic manner and notaccording to a set schedule. For example, data may be communicated fromsensor 104 using RFID technology when the sensor electronics are broughtinto communication range of reader device 120. Until communicated toreader device 120, data may remain stored in a memory of sensor 104.Thus, a user does not have to maintain close proximity to reader device120 at all times, and can instead upload data at a convenient time. Inyet other embodiments, a combination of automatic and non-automatic datatransfer may be implemented. For example, data transfer may continue onan automatic basis until reader device 120 is no longer in communicationrange of sensor 104.

An introducer may be present transiently to promote introduction ofsensor 104 into a tissue. In illustrative embodiments, the introducermay comprise a needle or similar sharp. It is to be recognized thatother types of introducers, such as sheaths or blades, may be present inalternative embodiments. More specifically, the needle or otherintroducer may transiently reside in proximity to sensor 104 prior totissue insertion and then be withdrawn afterward. While present, theneedle or other introducer may facilitate insertion of sensor 104 into atissue by opening an access pathway for sensor 104 to follow. Forexample, the needle may facilitate penetration of the epidermis as anaccess pathway to the dermis to allow implantation of sensor 104 to takeplace, according to one or more embodiments. After opening the accesspathway, the needle or other introducer may be withdrawn so that it doesnot represent a sharps hazard. In illustrative embodiments, suitableneedles may be solid or hollow, beveled or non-beveled, and/or circularor non-circular in cross-section. In more particular embodiments,suitable needles may be comparable in cross-sectional diameter and/ortip design to an acupuncture needle, which may have a cross-sectionaldiameter of about 250 microns. It is to be recognized, however, thatsuitable needles may have a larger or smaller cross-sectional diameterif needed for particular applications.

In some embodiments, a tip of the needle (while present) may be angledover the terminus of sensor 104, such that the needle penetrates atissue first and opens an access pathway for sensor 104. In otherillustrative embodiments, sensor 104 may reside within a lumen or grooveof the needle, with the needle similarly opening an access pathway forsensor 104. In either case, the needle is subsequently withdrawn afterfacilitating sensor insertion.

Referring now to FIGS. 2A-2C, particular enzyme systems that may be usedfor detecting ketones according to the disclosure herein will bedescribed in further detail. In the depicted enzymatic reactions,β-hydroxybutyrate serves as a surrogate for ketones formed in vivo. Asshown in FIG. 2A, one pair of concerted enzymes that may be used fordetecting ketones according to the disclosure herein isβ-hydroxybutyrate dehydrogenase (HBDH) and diaphorase, which may bedeposited within a ketones-responsive active area upon the surface of atleast one working electrode, as described further herein. When aketones-responsive active area contains this pair of concerted enzymes,β-hydroxybutyrate dehydrogenase may convert β-hydroxybutyrate andoxidized nicotinamide adenine dinucleotide (NAD⁺) into acetoacetate andreduced nicotinamide adenine dinucleotide (NADH), respectively. Theenzyme cofactors NAD⁺ and NADH aid in promoting the concerted enzymaticreactions disclosed herein. The NADH may then undergo oxidation underdiaphorase mediation, with the electrons transferred during this processproviding the basis for ketone detection at the working electrode. Thus,there is a 1:1 molar correspondence between the amount of electronstransferred to the working electrode and the amount of β-hydroxybutyrateconverted, thereby providing the basis for ketones detection andquantification based upon the measured amount of current at the workingelectrode. Transfer of the electrons resulting from NADH oxidation tothe working electrode may take place through an electron transfer agent,such as an osmium (Os) compound, as described further below. Albumin maybe present as a stabilizer with this pair of concerted enzymes.According to particular embodiments, the β-hydroxybutyrate dehydrogenaseand the diaphorase may be covalently bonded to a polymer within theketones-responsive active area of the analyte sensors. The NAD⁺ may ormay not be covalently bonded to the polymer, but if the NAD⁺ is notcovalently bonded, it may be physically retained within theketones-responsive active area. A membrane overcoating theketones-responsive active area may aid in retaining the NAD⁺ within theketones-responsive active area while still permitting sufficient inwarddiffusion of ketones to permit detection thereof. Suitable membranepolymers for overcoating the ketones-responsive active area arediscussed further herein.

Other suitable chemistries for enzymatically detecting ketones are shownin FIGS. 2B and 2C. In both instances, there is again a 1:1 molarcorrespondence between the amount of electrons transferred to theworking electrode and the amount of β-hydroxybutyrate converted, therebyproviding the basis for ketones detection.

As shown in FIG. 2B, β-hydroxybutyrate dehydrogenase (HBDH) may againconvert β-hydroxybutyrate and NAD⁺ into acetoacetate and NADH,respectively. Instead of electron transfer to the working electrodebeing completed by diaphorase (see FIG. 2A) and a transition metalelectron transfer agent, the reduced form of NADH oxidase (NADHOx (Red))undergoes a reaction to form the corresponding oxidized form (NADHOx(Ox)). NADHOx (Red) may then reform through a reaction with molecularoxygen to produce superoxide, which may undergo subsequent conversion tohydrogen peroxide under superoxide dismutase (SOD) mediation. Thehydrogen peroxide may then undergo oxidation at the working electrode toprovide a signal that may be correlated to the amount of ketones thatwere initially present. The SOD may be covalently bonded to a polymer inthe ketones-responsive active area, according to various embodiments.Like the enzyme system shown in FIG. 2A, the β-hydroxybutyratedehydrogenase and the NADH oxidase may be covalently bonded to a polymerin the ketones-responsive active area, and the NAD may or may not becovalently bonded to a polymer in the ketones-responsive active area. Ifthe NAD⁺ is not covalently bonded, it may be physically retained withinthe ketones-responsive active area, with a membrane polymer promotingretention of the NAD⁺ within the ketones-responsive active area.

As shown in FIG. 2C, another enzymatic detection chemistry for ketonesmay utilize β-hydroxybutyrate dehydrogenase (HBDH) to convertp-hydroxybutyrate and NAD⁺ into acetoacetate and NADH, respectively. Theelectron transfer cycle in this case is completed by oxidation ofpoly-1,10-phenanthroline-5,6-dione at the working electrode to reformNAD. The poly-1,10-phenanthroline-5,6-dione may or may not be covalentlybonded to a polymer within the ketones-responsive active area. Like theenzyme system shown in FIG. 2A, the β-hydroxybutyrate dehydrogenase maybe covalently bonded to a polymer in the ketones-responsive active area,and the NAD may or may not be covalently bonded to a polymer in theketones-responsive active area. Inclusion of an albumin in the activearea may provide a surprising improvement in response stability. Asuitable membrane polymer may promote retention of the NAD⁺ within theketones-responsive active area.

The glucose-responsive active areas in the analyte sensors disclosedherein may be physically adsorbed to a working electrode surface and maycomprise a glucose-responsive enzyme, such as glucose oxidase or glucosedehydrogenase. The glucose-responsive active area may comprise a polymerthat is covalently bound to the glucose-responsive enzyme, according tovarious embodiments. Suitable polymers for inclusion in the active areasare described below.

The analyte sensors disclosed herein may feature active areas ofdifferent types (i.e., a glucose-responsive active area and aketones-responsive active area) upon a single working electrode or upontwo or more separate working electrodes. Single working electrode sensorconfigurations may employ two-electrode or three-electrode detectionmotifs, according to various embodiments of the present disclosure andas described further herein. Sensor configurations featuring a singleworking electrode are described hereinafter in reference to FIGS. 3A-3C.Each of these sensor configurations may suitably incorporate aglucose-responsive active area and a ketones-responsive active areaaccording to various embodiments of the present disclosure. Sensorconfigurations featuring multiple working electrodes are describedthereafter in reference to FIGS. 4 and 5A-5D. When multiple workingelectrodes are present, a ketones-responsive active area may be disposedupon a first working electrode and a glucose-responsive active area maybe disposed upon a second working electrode. Sensor configurationsemploying multiple working electrodes may be particularly advantageousfor incorporating both a glucose-responsive active area and aketones-responsive active area according to the disclosure herein, sincemass transport limiting membranes having differing compositions and/ordifferent permeability values may be deposited more readily duringmanufacturing when the active areas are separated and/or spaced apart inthis manner. Particular sensor configurations featuring multiple workingelectrodes disposed in a manner to facilitate deposition of masstransport limiting membranes having differing compositions, particularlyby dip coating, upon each working electrode are shown in FIGS. 5A-5D.Suitable techniques for depositing the mass transport limiting membranesdisclosed herein include, for example, spray coating, painting, inkjetprinting, stenciling, roller coating, dip coating, or the like, and anycombination thereof.

When a single working electrode is present in an analyte sensor,three-electrode sensor configurations may comprise a working electrode,a counter electrode, and a reference electrode. Related two-electrodesensor configurations may comprise a working electrode and a secondelectrode, in which the second electrode may function as both a counterelectrode and a reference electrode (i.e., a counter/referenceelectrode). In both two-electrode and three-electrode sensorconfigurations, both the glucose-responsive active area and theketones-responsive active area may be disposed upon the single workingelectrode. In some embodiments, the various electrodes may be at leastpartially stacked (layered) upon one another and/or laterally spacedapart from one another upon the sensor tail. Suitable sensorconfigurations may be substantially flat in shape or substantiallycylindrical in shape, with the glucose-responsive active area and theketones-responsive active area being laterally spaced apart upon theworking electrode. In all of the sensor configurations disclosed herein,the various electrodes may be electrically isolated from one another bya dielectric material or similar insulator.

Analyte sensors featuring multiple working electrodes may similarlycomprise at least one additional electrode. When one additionalelectrode is present, the one additional electrode may function as acounter/reference electrode for each of the multiple working electrodes.When two additional electrodes are present, one of the additionalelectrodes may function as a counter electrode for each of the multipleworking electrodes and the other of the additional electrodes mayfunction as a reference electrode for each of the multiple workingelectrodes.

Analyte sensor configurations having a single working electrode will nowbe described in further detail. FIG. 3A shows a cross-sectional diagramof an illustrative two-electrode analyte sensor configuration having asingle working electrode, which is compatible for use in someembodiments of the disclosure herein. As shown, analyte sensor 200comprises substrate 212 disposed between working electrode 214 andcounter/reference electrode 216. Alternately, working electrode 214 andcounter/reference electrode 216 may be located upon the same side ofsubstrate 212 with a dielectric material interposed in between(configuration not shown). Active areas 218 a and 218 b (i.e., aglucose-responsive active area and a ketones-responsive active area) arelaterally spaced apart from one another upon the surface of workingelectrode 214. In the various sensor configurations shown herein, activeareas 218 a and 218 b may comprise multiple spots or a single spotconfigured for detection of each analyte. Analyte sensor 200 may beoperable for assaying glucose and ketones by any of coulometric,amperometric, voltammetric, or potentiometric electrochemical detectiontechniques.

Referring still to FIG. 3A, membrane 220 overcoats at least active areas218 a and 218 b and may optionally overcoat some or all of workingelectrode 214 and/or counter/reference electrode 216, or the entirety ofanalyte sensor 200. One or both faces of analyte sensor 200 may beovercoated with membrane 220. Membrane 220 may comprise one or morepolymeric membrane materials (membrane polymers) having suitablecapabilities for limiting analyte flux to active areas 218 a and 218 b.Although not readily apparent in FIG. 3A, the composition of membrane220 may vary at active areas 218 a and 218 b in order to differentiallyregulate the analyte flux at each location, as described further herein.For example, membrane 220 may be sprayed and/or printed onto activeareas 218 a and 218 b, such that the composition of membrane 220 differsat each location. In another alternative, membrane 220 may be depositedby dip coating starting from end A of analyte sensor 200. Specifically,end A of analyte sensor 200 may be dipped in a first coating formulationto overcoat active area 218 a. After partially curing the first coatingformulation upon active area 218 a, end A of analyte sensor 200 may bedipped in a second coating formulation to overcoat both active areas 218a and 218 b with the second coating formulation. As such, membrane 220may be continuous and feature a bilayer at active area 218 a and behomogeneous at active area 218 b.

FIGS. 3B and 3C show cross-sectional diagrams of illustrativethree-electrode sensor configurations having a single working electrode,which are compatible for use in some embodiments of the disclosureherein. Three-electrode sensor configurations featuring a single workingelectrode may be similar to that shown for analyte sensor 200 in FIG.3A, except for the inclusion of additional electrode 217 in analytesensors 201 and 202 (FIGS. 3B and 3C). With additional electrode 217,electrode 216 may then function as either a counter electrode or areference electrode, and additional electrode 217 may fulfill the otherelectrode function not otherwise accounted for. Working electrode 214continues to fulfill its original function in either case. Additionalelectrode 217 may be disposed upon either working electrode 214 orelectrode 216, with a separating layer of dielectric material in betweeneach. For example, as depicted in FIG. 3B, electrodes 214, 216 and 217are located upon the same face of substrate 212 and are electricallyisolated from one another by dielectric layers 219 a, 219 b and 219 c inbetween. Alternately, at least one of electrodes 214, 216 and 217 may belocated upon opposite faces of substrate 212, as shown in FIG. 3C. Thus,in some embodiments, electrode 214 (working electrode) and electrode 216(counter electrode) may be located upon opposite faces of substrate 212,with electrode 217 (reference electrode) being located upon one ofelectrodes 214 or 216 and spaced apart therefrom with a dielectricmaterial. Reference material layer 230 (e.g., Ag/AgCl) may be presentupon electrode 217, with the location of reference material layer 230not being limited to that depicted in FIGS. 3B and 3C. As with analytesensor 200 shown in FIG. 3A, active areas 218 a and 218 b in analytesensors 201 and 202 are disposed laterally spaced apart from one anotherupon working electrode 214 in the sensor configurations of FIGS. 3B and3C. Like analyte sensor 200, analyte sensors 201 and 202 may be operablefor assaying glucose and ketones by any of coulometric, amperometric,voltammetric, or potentiometric electrochemical detection techniques.

Also like analyte sensor 200, membrane 220 may also overcoat activeareas 218 a and 218 b, as well as other sensor components, in analytesensors 201 and 202. Additional electrode 217 may be overcoated withmembrane 220 in some embodiments. Although FIGS. 3B and 3C have depictedall of electrodes 214, 216 and 217 as being overcoated with membrane220, it is to be recognized that only working electrode 214 or activeareas 218 a and 218 b may be overcoated in some embodiments. Althoughnot apparent in FIGS. 3B and 3C, the thickness of membrane 220 may bethe same or different at various locations, such as varying thicknessesat active areas 218 a and 218 b. Likewise, membrane 220 may also varycompositionally at active areas 218 a and 218 b in order todifferentially regulate the analyte flux at each location. For example,dip coating from end A of analyte sensors 201 and 202 may be used todeposit a continuous membrane featuring a bilayer membrane portion atactive area 218 a and a homogeneous membrane portion at active area 218b, as described in more detail above for FIG. 3A. As in two-electrodeanalyte sensor configurations (FIG. 3A), one or both faces of analytesensors 201 and 202 may be overcoated with membrane 220 in the sensorconfigurations of FIGS. 3B and 3C, or the entirety of analyte sensors201 and 202 may be overcoated. Accordingly, the three-electrode sensorconfigurations shown in FIGS. 3B and 3C should be understood as beingillustrative and non-limiting of the disclosure herein, with alternativeelectrode and/or layer configurations residing within the scope of thepresent disclosure.

Sensor configurations having multiple working electrodes, specificallytwo working electrodes, will now be described in further detail inreference to FIGS. 4 and 5A-5D. Although the following description isprimarily directed to sensor configurations having two workingelectrodes, it is to be appreciated that more than two workingelectrodes may be incorporated through extension of the disclosureherein. Additional working electrodes may be used to impart additionalsensing capabilities to the analyte sensors beyond just glucose andketones sensing.

FIG. 4 shows a cross-sectional diagram of an illustrative analyte sensorconfiguration having two working electrodes, a reference electrode and acounter electrode, which is compatible for use in some embodiments ofthe disclosure herein. As shown in FIG. 4 , analyte sensor 300 includesworking electrodes 304 and 306 disposed upon opposite faces of substrate302. Active area 310 a is disposed upon the surface of working electrode304, and active area 310 b is disposed upon the surface of workingelectrode 306. Active areas 310 a and 310 b may be glucose-responsiveand ketones-responsive, according to various embodiments of the presentdisclosure. Counter electrode 320 is electrically isolated from workingelectrode 304 by dielectric layer 322, and reference electrode 321 iselectrically isolated from working electrode 306 by dielectric layer323. Outer dielectric layers 330 and 332 are positioned upon referenceelectrode 321 and counter electrode 320, respectively. Membrane 340 hasfirst membrane portion 340 a and second membrane portion 340 b, whichseparately overcoat at least active areas 310 a and 310 b, respectively,according to various embodiments, with other components of analytesensor 300 or the entirety of analyte sensor 300 optionally beingovercoated with first membrane portion 340 a and/or second membraneportion 340 b as well. Again, membrane 340 may be continuous but varycompositionally within first membrane portion 340 a and second membraneportion 340 b (i.e., upon active areas 310 a and 310 b) in order toafford different permeability values for differentially regulating theanalyte flux at each location. For example, different membraneformulations may be sprayed and/or printed onto the opposing faces ofanalyte sensor 300. Dip coating techniques may also be appropriate,particularly for depositing at least a portion of a bilayer membraneupon one of active areas 310 a and 310 b. Accordingly, one of firstmembrane portion 340 a and second membrane portion 340 b may comprise abilayer membrane and the other of first membrane portion 340 a andsecond membrane portion 340 b may comprise a single membrane polymer,according to particular embodiments of the present disclosure. Likeanalyte sensors 200, 201 and 202, analyte sensor 300 may be operable forassaying glucose and ketones by any of coulometric, amperometric,voltammetric, or potentiometric electrochemical detection techniques.

Alternative sensor configurations having multiple working electrodes anddiffering from that shown in FIG. 4 may feature a counter/referenceelectrode instead of separate counter and reference electrodes 320,321,and/or feature layer and/or membrane arrangements varying from thoseexpressly depicted. For example, the positioning of counter electrode320 and reference electrode 321 may be reversed from that depicted inFIG. 4 . In addition, working electrodes 304 and 306 need notnecessarily reside upon opposing faces of substrate 302 in the mannershown in FIG. 4 .

Although suitable sensor configurations may feature electrodes that aresubstantially planar in character, it is to be appreciated that sensorconfigurations featuring non-planar electrodes may be advantageous andparticularly suitable for use in the disclosure herein. In particular,substantially cylindrical electrodes that are disposed concentricallywith one another may facilitate deposition of a mass transport limitingmembrane, as described hereinbelow. FIGS. 5A-5D show perspective viewsof analyte sensors featuring substantially cylindrical electrodes thatare disposed concentrically with respect to one another. Although FIGS.5A-5D have depicted sensor configurations featuring two workingelectrodes, it is to be appreciated that similar sensor configurationshaving either one working electrode or more than two working electrodesare possible through extension of the disclosure herein.

FIG. 5A shows a perspective view of an illustrative sensor configurationin which multiple electrodes are substantially cylindrical and aredisposed concentrically with respect to one another about a centralsubstrate. As shown, analyte sensor 400 includes central substrate 402about which all electrodes and dielectric layers are disposedconcentrically with respect to one another. In particular, workingelectrode 410 is disposed upon the surface of central substrate 402, anddielectric layer 412 is disposed upon a portion of working electrode 410distal to sensor tip 404. Working electrode 420 is disposed upondielectric layer 412, and dielectric layer 422 is disposed upon aportion of working electrode 420 distal to sensor tip 404. Counterelectrode 430 is disposed upon dielectric layer 422, and dielectriclayer 432 is disposed upon a portion of counter electrode 430 distal tosensor tip 404. Reference electrode 440 is disposed upon dielectriclayer 432, and dielectric layer 442 is disposed upon a portion ofreference electrode 440 distal to sensor tip 404. As such, exposedsurfaces of working electrode 410, working electrode 420, counterelectrode 430, and reference electrode 440 are spaced apart from oneanother along longitudinal axis B of analyte sensor 400. Spacing apartof working electrode 410 and working electrode 420 along a longitudinalaxis may also be realized in substantially planar sensor configurationsas well, such as those provided above.

Referring still to FIG. 5A, active areas 414 a and 414 b are disposedupon the exposed surfaces of working electrodes 410 and 420,respectively, thereby allowing contact with a fluid to take place forsensing of glucose and/or ketones to take place. Although active areas414 a and 414 b have been depicted as three discrete spots in FIG. 5A,it is to be appreciated that fewer or greater than three spots may bepresent in alternative sensor configurations. Each of active areas 414 aand 414 b can also be a continuous layer that is disposed as a ring uponthe exposed surface of working electrodes 410 and 420, respectively.

Similar to the sensor configuration discussed above, at least workingelectrodes 410 and 420 and active areas 414 a and 414 b thereon areovercoated with a membrane in the sensor configuration of FIG. 5A.Although a membrane featuring a single composition may overcoat activeareas 414 a and 414 b, the membrane compositions may differcompositionally in each location in order to afford differentpermeability values, thereby levelizing the sensor response for eachanalyte. In the sensor configuration depicted in FIG. 5A, membraneportion 450 having a first composition overcoats working electrode 410and active area 414 a, along with optional overcoating of dielectriclayer 412, and membrane portion 451 having a second compositiondiffering from the first composition overcoats working electrode 420 andactive area 414 b, along with optional overcoating of dielectric layer412 and/or dielectric layer 422. Although not shown in FIG. 5A, counterelectrode 430, reference electrode 440, and dielectric layers 432 and442 may also be overcoated with membrane 451.

FIG. 5B shows an alternative sensor configuration to that depicted inFIG. 5A, in which all components upon the sensor tail aremembrane-coated. In the sensor configuration shown in FIG. 5B, sensor401 contains working electrode 410, active area 414 a, and dielectriclayer 412 that are each overcoated with first portion 452 a of membrane452. First portion 452 a comprises two membrane layers, thereby defininga bilayer membrane. Second portion 452 b of membrane 452 overcoatsworking electrode 420, active area 414 b, and the remainder of thesensor tail (i.e., counter electrode 430, reference electrode 440, anddielectric layers 422, 432 and 442) with a single membrane polymer.While shown as having two portions 452 a and 452 b, it is to beappreciated that additional portions may be present. Moreover, firstportion 452 a may be a bilayer membrane, as depicted, or a homogenousadmixture of multiple membrane polymers. Sensor configurations havingfirst portion 452 a as a bilayer membrane may feature an active area 414a that is ketones-responsive and an active area 414 b that isglucose-responsive, according to various embodiments of the presentdisclosure. Further details regarding suitable membrane polymers andtechniques for deposition of first and second portions 452 a,452 b ofmembrane 452 at each location are provided hereinbelow.

It is to be further appreciated that the positioning of the variouselectrodes in FIGS. 5A and 5B may differ from that expressly depicted.For example, the positions of counter electrode 430 and referenceelectrode 440 may be reversed from the depicted configurations in FIGS.5A and 5B. Similarly, the positions of working electrodes 410 and 420are not limited to those that are expressly depicted in FIGS. 5A and 5B.FIG. 5C shows an alternative sensor configuration to that shown in FIG.5B, in which sensor 405 contains counter electrode 430 and referenceelectrode 440 that are located more proximal to sensor tip 404 andworking electrodes 410 and 420 that are located more distal to sensortip 404. Sensor configurations in which working electrodes 410 and 420are located more distal to sensor tip 404 may be advantageous byproviding a larger surface area for deposition of active areas 414 a and414 b (five discrete sensing spots illustratively shown in FIG. 5C),thereby facilitating an increased signal strength in some cases. Thelocations of the bilayer membrane defined by first portion 452 a and thehomogeneous membrane defined by second portion 452 b have been similarlyadjusted to accommodate the change in location of working electrodes 410and 420.

Although FIGS. 5A-5C have depicted sensor configurations that are eachsupported upon central substrate 402, it is to be appreciated thatalternative sensor configurations may be electrode-supported instead andlack central substrate 402. In particular, the innermost concentricelectrode may be utilized to support the other electrodes and dielectriclayers. FIG. 5D shows an alternative sensor configuration to thatdepicted in FIG. 5C, in which sensor 406 does not contain centralsubstrate 402 and counter electrode 430 is the innermost concentricelectrode and is employed for disposing reference electrode 440, workingelectrodes 410 and 420, and dielectric layers 432, 442, 412, and 422sequentially thereon. In view of the disclosure herein, it is again tobe appreciated that other electrode and dielectric layer configurationsmay be employed in sensor configurations lacking central substrate 402.As such, the sensor configuration depicted in FIG. 5D should beconsidered illustrative in nature and non-limiting.

Accordingly, some embodiments of analyte sensors disclosed herein maycomprise a sensor tail comprising at least a working electrode, aglucose-responsive active area comprising a glucose-responsive enzymedisposed upon a surface of the working electrode and aketones-responsive active area disposed upon the surface of the workingelectrode and spaced apart from the glucose-responsive active area. Theketones-responsive active area comprises an enzyme system comprising atleast two enzymes that are capable of acting in concert to facilitatedetection of ketones. Each active area has an oxidation-reductionpotential, and the oxidation-reduction potential of theglucose-responsive active area is sufficiently separated from theoxidation-reduction potential of the ketones-responsive active area toallow independent production of a signal from one of theglucose-responsive active area or the ketones-responsive active area.

When the glucose-responsive active area and the ketones-responsiveactive area are arranged upon a single working electrode in this manner,one of the active areas may be configured such that it can beinterrogated separately to facilitate detection of each analyte, asdescribed hereinafter. That is, either the glucose-responsive activearea or the ketones-responsive active area may produce a signalindependently of the other active area.

Some or other embodiments of analyte sensors disclosed herein mayfeature the glucose-responsive active area and the ketones-responsiveactive area upon the surface of different working electrodes. Suchanalyte sensors may comprise a sensor tail comprising at least a firstworking electrode and a second working electrode, a ketones-responsiveactive area disposed upon a surface of the first working electrode, aglucose-responsive active area comprising a glucose-responsive enzymedisposed upon a surface of the second working electrode, and a membranehaving a first portion overcoating the ketones-responsive active areaand a second portion overcoating the glucose-responsive active area, inwhich the first portion and the second portion have differentcompositions.

In particular embodiments, the first portion is multi-component andcomprises at least a first membrane polymer and a second membranepolymer that differ from one another, and the second portion ishomogeneous and comprises one of the first membrane polymer and thesecond membrane polymer.

According to various embodiments of the present disclosure, an electrontransfer agent may be present in the glucose-responsive active area andthe ketones-responsive active area in any of the illustrative sensorconfigurations disclosed herein. Suitable electron transfer agents mayfacilitate conveyance of electrons to the adjacent working electrodeafter either analyte undergoes an enzymatic oxidation-reduction reactionwithin the corresponding active area, thereby generating a current thatis indicative of the presence of that particular analyte. The amount ofcurrent generated is proportional to the quantity of analyte that ispresent. Depending on the sensor configuration used, the electrontransfer agents in the glucose-responsive active area and theketones-responsive active area may be the same or different. Forexample, when the glucose-responsive active area and theketones-responsive active area are disposed upon the same workingelectrode, the electron transfer agent within each active area may bedifferent (e.g., chemically different such that the electron transferagents exhibit different oxidation-reduction potentials). When multipleworking electrodes are present, the electron transfer agent within eachactive area may be the same or different, since each working electrodemay be interrogated separately.

According to various embodiments of the present disclosure, suitableelectron transfer agents may include electroreducible andelectrooxidizable ions, complexes or molecules (e.g., quinones) havingoxidation-reduction potentials that are a few hundred millivolts aboveor below the oxidation-reduction potential of the standard calomelelectrode (SCE). According to some embodiments, suitable electrontransfer agents may include low-potential osmium complexes, such asthose described in U.S. Pat. Nos. 6,134,461 and 6,605,200, which areincorporated herein by reference in their entirety. Additional examplesof suitable electron transfer agents include those described in U.S.Pat. Nos. 6,736,957, 7,501,053 and 7,754,093, the disclosures of each ofwhich are incorporated herein by reference in their entirety. Othersuitable electron transfer agents may comprise metal compounds orcomplexes of ruthenium, osmium, iron (e.g., polyvinylferrocene orhexacyanoferrate), or cobalt, including metallocene compounds thereof,for example. Suitable ligands for the metal complexes may also include,for example, bidentate or higher denticity ligands such as, for example,bipyridine, biimidazole, phenanthroline, or pyridyl(imidazole). Othersuitable bidentate ligands may include, for example, amino acids, oxalicacid, acetylacetone, diaminoalkanes, or o-diaminoarenes. Any combinationof monodentate, bidentate, tridentate, tetradentate, or higher denticityligands may be present in a metal complex to achieve a full coordinationsphere.

Active areas suitable for detecting glucose and ketones may alsocomprise a polymer to which the electron transfer agents are covalentlybound. Any of the electron transfer agents disclosed herein may comprisesuitable functionality to promote covalent bonding to the polymer withinthe active areas. Suitable examples of polymer-bound electron transferagents may include those described in U.S. Pat. Nos. 8,444,834,8,268,143 and 6,605,201, the disclosures of which are incorporatedherein by reference in their entirety. Suitable polymers for inclusionin the active areas may include, but are not limited to,polyvinylpyridines (e.g., poly(4-vinylpyridine)), polyvinylimidazoles(e.g., poly(1-vinylimidazole)), or any copolymer thereof. Illustrativecopolymers that may be suitable for inclusion in the active areasinclude those containing monomer units such as styrene, acrylamide,methacrylamide, or acrylonitrile, for example. The polymer within eachactive area may be the same or different.

In particular embodiments of the present disclosure, the mass transportlimiting membrane overcoating each active area may comprise at least acrosslinked polyvinylpyridine homopolymer or copolymer. The compositionof the mass transport limiting membrane may be the same or differentwhere the mass transport limiting membrane overcoats each active area.In particular embodiments, the portion of the mass transport limitingmembrane overcoating the glucose-responsive active area may besingle-component (contain a single membrane polymer) and the portion ofthe mass transport limiting membrane overcoating the ketones-responsiveactive area may be multi-component (contain two or more differentmembrane polymers, one of which is a polyvinylpyridine homopolymer orcopolymer). The multicomponent membrane may be present as a bilayermembrane or as a homogeneous admixture of the two or more membranepolymers. A homogeneous admixture may be deposited by combining the twoor more membrane polymers in a solution and then depositing the solutionupon a working electrode. In still more specific embodiments of thepresent disclosure, the glucose-responsive active area may be overcoatedwith a membrane comprising a polyvinylpyridine-co-styrene copolymer, andthe ketones-responsive active area may be overcoated with amulticomponent membrane comprising polyvinylpyridine andpolyvinylpyridine-co-styrene, either as a bilayer membrane or ahomogeneous admixture.

The manner of covalent bonding between the electron transfer agent andthe polymer comprising each active area is not considered to beparticularly limited. Covalent bonding of the electron transfer agent tothe polymer may take place by polymerizing a monomer unit bearing acovalently bound electron transfer agent, or the electron transfer agentmay be reacted with the polymer separately after the polymer has alreadybeen synthesized. According to some embodiments, a bifunctional spacermay covalently bond the electron transfer agent to the polymer withinthe active area, with a first functional group being reactive with thepolymer (e.g., a functional group capable of quaternizing a pyridinenitrogen atom or an imidazole nitrogen atom) and a second functionalgroup being reactive with the electron transfer agent (e.g., afunctional group that is reactive with a ligand coordinating a metalion).

Similarly, according to some or other various embodiments of the presentdisclosure, one or more of the enzymes within the active areas may becovalently bonded to the polymer. When an enzyme system comprisingmultiple enzymes is present in a given active area, all of the multipleenzymes may be covalently bonded to the polymer in some embodiments, andin other embodiments, only a portion of the multiple enzymes may becovalently bonded to the polymer. For example, one or more enzymescomprising an enzyme system may be covalently bonded to the polymer andat least one enzyme may be non-covalently associated with the polymer,such that the non-covalently bonded enzyme is physically entrainedwithin the polymer. According to more specific embodiments, covalentbonding of the enzyme(s) to the polymer in a given active area may takeplace via a crosslinker introduced with a suitable crosslinking agent.Suitable crosslinking agents for reaction with free amino groups in theenzyme (e.g., with the free side chain amine in lysine) may includecrosslinking agents such as, for example, polyethylene glycol diglycidylether (PEGDGE) or other polyepoxides, cyanuric chloride,N-hydroxysuccinimide, imidoesters, epichlorohydrin, or derivatizedvariants thereof. Suitable crosslinking agents for reaction with freecarboxylic acid groups in the enzyme may include, for example,carbodiimides. The crosslinking of the enzyme to the polymer isgenerally intermolecular, but can be intramolecular in some embodiments.

The electron transfer agent and/or the enzyme(s) may be associated withthe polymer in the active area through means other than covalent bondingas well. In some embodiments, the electron transfer agent and/or theenzyme(s) may be ionically or coordinatively associated with thepolymer. For example, a charged polymer may be ionically associated withan oppositely charged electron transfer agent or enzyme(s). In stillother embodiments, the electron transfer agent and/or the enzyme(s) maybe physically entrained within the polymer without being bonded thereto.Physically entrained electron transfer agents and/or enzyme(s) may stillsuitably interact with a fluid to promote analyte detection withoutbeing substantially leached from the active areas.

In particular embodiments, the glucose-responsive enzyme in theglucose-responsive active area may be covalently bonded to a polymer inthe glucose-responsive active area, in combination with an electrontransfer agent that is also covalently bonded to the polymer.

In other particular embodiments, at least a portion of the enzymes inthe enzyme system within the ketones-responsive active area may becovalently bonded to a polymer in the ketones-responsive active area, incombination with an electron transfer agent that is also covalentlybonded to the polymer. One suitable enzyme system that may be suitableto facilitate detection of ketones is p-hydroxybutyrate dehydrogenase(NADH), nicotinamide adenine dinucleotide (NAD⁺), and diaphorase (seeFIG. 2A). In particular embodiments of the present disclosure, theβ-hydroxybutyrate dehydrogenase and diaphorase may be covalently bondedto the polymer in the ketones-responsive active area, and the NAD⁺ maybe non-covalently associated with the polymer. The polymer within theketones-responsive active area may be chosen such that outward diffusionof the NAD⁺ is limited. The membrane polymer overcoating theketones-responsive active area may similarly limit outward diffusion ofNAD⁺ to promote a reasonable sensor lifetime (days to weeks) while stillallowing sufficient inward ketones diffusion to promote detection. Instill further embodiments, the components of the foregoing enzyme systemmay be covalently bonded or non-covalently associated with the polymerin the ketones-responsive active area as described previously, incombination with an electron transfer agent that is also covalentlybonded to the polymer.

The glucose-responsive and ketones-responsive active areas in theanalyte sensors disclosed herein may comprise one or more discrete spots(e.g., one to about ten spots, or even more discrete spots), which mayrange in size from about 0.01 mm² to about 1 mm², although larger orsmaller individual spots within the active areas are also contemplatedherein. Active areas defined as continuous bands around a cylindricalelectrode are also possible in the disclosure herein.

In more specific embodiments, analyte sensors of the present disclosuremay comprise a sensor tail that is configured for insertion into atissue. Suitable tissues are not considered to be particularly limitedand are addressed in more detail above. Similarly, considerations fordeploying a sensor tail at a particular position within a tissue areaddressed above.

In embodiments wherein the glucose-responsive active area and theketones-responsive active area are arranged upon a single workingelectrode, the oxidation-reduction potential associated with theglucose-responsive active area may be separated from theoxidation-reduction potential of the ketones-responsive active area byat least about 100 mV, or by at least about 150 mV, or by at least about200 mV. The upper limit of the separation between theoxidation-reduction potentials is dictated by the workingelectrochemical window in vivo. By having the oxidation-reductionpotentials of the two active areas sufficiently separated in magnitudefrom one another, an electrochemical reaction make take place within oneof the two active areas (i.e., within the glucose-responsive active areaor the ketones-responsive active area) without substantially inducing anelectrochemical reaction within the other active area. Thus, a signalfrom one of the glucose-responsive active area or the ketones-responsiveactive area may be independently produced at or above its correspondingoxidation-reduction potential (the lower oxidation-reduction potential)but below the oxidation-reduction potential of the other of theglucose-responsive active area and the ketones-responsive active area(the higher oxidation-reduction potential). At or above theoxidation-reduction potential (the higher oxidation-reduction potential)of the other active area that was not previously interrogated, incontrast, electrochemical reactions may occur within both theglucose-responsive active area and the ketones-responsive active area.As such, the resulting signal at or above the higher oxidation-reductionpotential may include a signal contribution from both theglucose-responsive active area and the ketones-responsive active area,and the observed signal is a composite signal. The signal contributionfrom one active area (either the glucose-responsive active area or theketones-responsive active area) at or above its oxidation-reductionpotential may then be determined by subtracting from the compositesignal the signal obtained solely from either the glucose-responsiveactive area or the ketones-responsive active area at or above itscorresponding oxidation-reduction potential.

In more specific embodiments, the glucose-responsive active area and theketones-responsive active area may contain different electron transferagents when the active areas are located upon the same workingelectrode, so as to afford oxidation-reduction potentials that aresufficiently separated in magnitude from one another. More specifically,the glucose-responsive active area may comprise a first electrontransfer agent and the ketones-responsive active area may comprise asecond electron transfer agent, with the first and second electrontransfer agents being different. The metal center and/or the ligandspresent in a given electron transfer agent may be varied to providesufficient separation of the oxidation-reduction potentials within thetwo active areas, according to various embodiments of the presentdisclosure.

Ideally, glucose-responsive active areas and ketones-responsive activeareas located upon a single working electrode may be configured toattain a steady state current rapidly upon operating the analyte sensorat a given potential. Rapid attainment of a steady state current may bepromoted by choosing an electron transfer agent for each active areathat changes its oxidation state quickly upon being exposed to apotential at or above its oxidation-reduction potential. Making theactive areas as thin as possible may also facilitate rapid attainment ofa steady state current. For example, suitable thicknesses for theglucose-responsive active area and ketones-responsive active area mayrange from about 0.1 microns to about 10 microns. In some or otherembodiments, combining a conductive material such as, for example,carbon nanotubes, graphene, or metal nanoparticles within one or more ofthe active areas may promote rapid attainment of a steady state current.Suitable amounts of conductive particles may range from about 0.1% toabout 50% by weight of the active area, or from about 1% to about 50% byweight, or from about 0.1% to about 10% by weight, or from about 1% toabout 10% by weight. Stabilizers may also be employed to promoteresponse stability.

It is also to be appreciated that the sensitivity (output current) ofthe analyte sensors toward each analyte may be varied by changing thecoverage (area or size) of the active areas, the areal ratio of theactive areas with respect to one another, the identity, thickness and/orcomposition of a mass transport limiting membrane overcoating the activeareas. Variation of these parameters may be conducted readily by onehaving ordinary skill in the art once granted the benefit of thedisclosure herein.

Detection methods for assaying glucose and ketones employing analytesensors featuring a glucose-responsive active area and aketones-responsive active area upon a single working electrode maycomprise: exposing an analyte sensor to a fluid comprising at least oneof glucose and ketones. The analyte sensor comprises a sensor tailcomprising at least a working electrode, particularly a single workingelectrode, and at least a glucose-responsive active area and aketones-responsive active area disposed upon a surface of the workingelectrode and space apart from the glucose-responsive active area. Theglucose-responsive active area comprises a glucose-responsive enzyme anda polymer, and the ketones-responsive active area comprises an enzymesystem comprising two or more enzymes that are capable of acting inconcert to facilitate detection of ketones. Each active area has anoxidation-reduction potential, and the oxidation-reduction potential ofa first active area (e.g., either the glucose-responsive active area orthe ketones-responsive active area) is sufficiently separated from theoxidation-reduction potential of the other of the glucose-responsiveactive area or the ketones-responsive active area to allow production ofa signal from the first active area independent of production of asignal from the other active area. The methods additionally comprise:obtaining a first signal at or above a lower of the oxidation-reductionpotential and the second oxidation-reduction potential but below ahigher of the first oxidation-reduction potential and the secondoxidation-reduction potential, such that the first signal isproportional to a concentration of one of glucose or ketones in thefluid; obtaining a second signal at or above a higher of the firstoxidation-reduction potential and the second oxidation-reductionpotential, such that the second signal is a composite signal comprisinga signal contribution from the glucose-responsive active area and asignal contribution from the ketones-responsive active area; andsubtracting the first signal from the second signal to obtain adifference signal, the difference signal being proportional to aconcentration of one of glucose and ketones.

In more specific embodiments, the oxidation-reduction potentialassociated with the first active area may be separated from theoxidation-reduction potential of the second active area by at leastabout 100 mV, or by at least about 150 mV, or by at least about 200 mVin order to provide sufficient separation for independent production ofa signal from the first active area. In particular, theoxidation-reduction potentials of the first active area and the secondactive area may be separated by about 100 mV to about 500 mV, or about100 mV to about 400 mV, or about 100 mV to about 300 mV.

In some embodiments, the signals associated with each active area may becorrelated to a corresponding concentration of glucose or ketones byconsulting a lookup table or calibration curve for each analyte. Alookup table for each analyte may be populated by assaying multiplesamples having known analyte concentrations and recording the sensorresponse at each concentration for each analyte. Similarly, acalibration curve for each analyte may be determined by plotting theanalyte sensor response for each analyte as a function of theconcentration and determining a suitable calibration function over thecalibration range (e.g., by regression, particularly linear regression).

A processor may determine which sensor response value in a lookup tableis closest to that measured for a sample having an unknown analyteconcentration and then report the analyte concentration accordingly. Insome or other embodiments, if the sensor response value for a samplehaving an unknown analyte concentration is between the recorded valuesin the lookup table, the processor may interpolate between two lookuptable values to estimate the analyte concentration. Interpolation mayassume a linear concentration variation between the two values reportedin the lookup table. Interpolation may be employed when the sensorresponse differs a sufficient amount from a given value in the lookuptable, such as variation of about 10% or greater.

Likewise, according to some or other various embodiments, a processormay input the sensor response value for a sample having an unknownanalyte concentration into a corresponding calibration function. Theprocessor may then report the analyte concentration accordingly.

Detection methods for assaying glucose and ketones employing analytesensors featuring a glucose-responsive active area and aketones-responsive active area upon separate working electrodes maycomprise: exposing an analyte sensor to a fluid comprising at least oneof glucose and ketones. The analyte sensor comprises a sensor tailcomprising at least a first working electrode and second workingelectrode, a ketones-responsive active area disposed upon a surface ofthe first working electrode, a glucose-responsive active area disposedupon a surface of the second working electrode, and a membrane having afirst portion overcoating the ketones-responsive active area and asecond portion overcoating the glucose-responsive active area. Theglucose-responsive active area comprises a glucose-responsive enzyme,and the ketones-responsive active area comprises an enzyme systemcomprising at least two enzymes that are capable of acting in concert tofacilitate detection of ketones.

In particular embodiments, the first portion may be multi-component andcomprise at least a first membrane polymer and a second membrane polymerthat differ from one another, and the second portion may be homogeneousand comprise one of the first membrane polymer and the second membranepolymer. As such, the membrane overcoating the glucose-responsive activearea differs in composition from the multi-component membraneovercoating the ketones-responsive active area.

The methods additionally comprise applying a potential to the firstworking electrode and the second working electrode, obtaining a firstsignal at or above an oxidation-reduction potential of theglucose-responsive active area, in which the first signal isproportional to a concentration of glucose in the fluid, obtaining asecond signal at or above an oxidation-reduction potential of theketones-responsive active area, in which the second signal isproportional to a concentration of ketones in the fluid, and correlatingthe first signal to the concentration of glucose in the fluid and thesecond signal to the concentration of ketones in the fluid.

The first portion of the membrane may comprise an admixture of membranepolymers in some embodiments of the present disclosure or comprise abilayer membrane or other membrane structure having at least twomembrane layers in other embodiments of the present disclosure. When thefirst portion of the membrane comprises a bilayer membrane, the bilayermembrane may comprise a first membrane polymer disposed upon theketones-responsive active area, and a second membrane polymer disposedupon the first membrane polymer. The homogeneous membrane overcoatingthe glucose-responsive active area may comprise the second membranepolymer. That is, the first membrane polymer may be disposed directlyupon the ketones-responsive active area, and the second membrane polymermay be disposed upon the first membrane polymer and upon theglucose-responsive active area. Thus, the first portion of the membranemay be thicker than the second portion of the membrane. As discussedabove, bilayer membranes and homogeneous membranes of this type may bedeposited by dip coating of particular electrode configurations in someembodiments of the present disclosure. In particular embodiments of thepresent disclosure, the first portion of the membrane may comprisepolyvinylpyridine (PVP) and polyvinylpyridine-co-styrene, and secondportion of the membrane may comprise polyvinylpyridine-co-styrene.

According to more specific embodiments, the first signal and the secondsignal maybe measured at different times. Thus, in such embodiments, apotential may be alternately applied to the first working electrode andthe second working electrode. In other specific embodiments, the firstsignal and the second signal may be measured simultaneously via a firstchannel and a second channel, in which case a potential may be appliedto both electrodes at the same time. In either case, the signalassociated with each active area may then be correlated to theconcentration of glucose and ketones using a lookup table or acalibration function in a similar manner to that discussed above.

Embodiments disclosed herein include:

A. Analyte sensors responsive to glucose and ketones. The analytesensors comprise: a sensor tail comprising at least a working electrode;a glucose-responsive active area comprising a glucose-responsive enzymedisposed upon a surface of the working electrode; a ketones-responsiveactive area disposed upon the surface of the working electrode andspaced apart from the glucose-responsive active area, theketones-responsive active area comprising an enzyme system comprising atleast two enzymes that are capable of acting in concert to facilitatedetection of ketones; wherein each active area has anoxidation-reduction potential, and the oxidation-reduction potential ofthe glucose-responsive active area is sufficiently separated from theoxidation-reduction potential of the ketones-responsive active area toallow independent production of a signal from one of theglucose-responsive active area or the ketones-responsive active area.

B. Methods for assaying glucose and ketones using a single analytesensor. The methods comprise: exposing an analyte sensor to a fluidcomprising at least one of glucose and ketones; wherein the analytesensor comprises a sensor tail comprising at least a working electrode,a glucose-responsive active area having a first oxidation-reductionpotential disposed upon a surface of the working electrode, and aketones-responsive active area having a second oxidation-reductionpotential disposed upon the surface of the working electrode and spacedapart from the glucose-responsive active area; wherein theglucose-responsive active area comprises a glucose-responsive enzyme,the ketones-responsive active area comprises an enzyme system comprisingat least two enzymes that are capable of acting in concert to facilitatedetection of ketones, and the first oxidation-reduction potential andthe second oxidation-reduction potential are sufficiently separated fromone another to allow independent production of a signal from one of theglucose-responsive active area or the ketones-responsive active area;obtaining a first signal at or above a lower of the firstoxidation-reduction potential and the second oxidation-reductionpotential but below a higher of the first oxidation-reduction potentialand the second oxidation-reduction potential, the first signal beingproportional to a concentration of one of glucose or ketones in thefluid; obtaining a second signal at or above a higher of the firstoxidation-reduction potential and the second oxidation-reductionpotential, the second signal being a composite signal comprising a firstsignal contribution from the glucose-responsive active area and a secondsignal contribution from the ketones-responsive active area; andsubtracting the first signal from the second signal to obtain adifference signal, the difference signal being proportional to aconcentration of one of glucose or ketones in the fluid.

C. Analyte sensors responsive to glucose and ketones and having twoworking electrodes. The analyte sensors comprise: a sensor tailcomprising at least a first working electrode and a second workingelectrode; a glucose-responsive active area comprising aglucose-responsive enzyme disposed upon a surface of the first workingelectrode; a ketones-responsive active area disposed upon a surface ofthe second working electrode, the ketones-responsive active areacomprising an enzyme system comprising at least two enzymes that arecapable of acting in concert to facilitate detection of ketones; a firstmembrane overcoating the ketones-responsive active area, and a secondmembrane overcoating the glucose-responsive active area; wherein thefirst membrane and the second membrane have differing permeabilityvalues.

D. Methods for assaying glucose and ketones using a single analytesensor having two working electrodes. The methods comprise: exposing ananalyte sensor to a fluid comprising at least one of glucose andketones; wherein the analyte sensor comprises a sensor tail comprisingat least a first working electrode and second working electrode, aglucose-responsive active area disposed upon a surface of the firstworking electrode, a ketones-responsive active area disposed upon asurface of the second working electrode, and a first membraneovercoating the ketones-responsive active area, and a second membraneovercoating the glucose-responsive active area; wherein the firstmembrane and the second membrane have differing permeability values;wherein the glucose-responsive active area comprises aglucose-responsive enzyme, and the ketones-responsive active areacomprises an enzyme system comprising at least two enzymes that arecapable of acting in concert to facilitate detection of ketones;applying a potential to the first working electrode and the secondworking electrode; obtaining a first signal at or above anoxidation-reduction potential of the glucose-responsive active area, thefirst signal being proportional to a concentration of glucose in thefluid; obtaining a second signal at or above an oxidation-reductionpotential of the ketones-responsive active area, the second signal beingproportional to a concentration of ketones in the fluid; and correlatingthe first signal to the concentration of glucose in the fluid and thesecond signal to the concentration of ketones in the fluid.

Each of embodiments A-D may have one or more of the following additionalelements in any combination:

Element 1: wherein the sensor tail is configured for insertion into atissue.

Element 2: wherein the oxidation-reduction potential of theglucose-responsive active area is separated from the oxidation-reductionpotential of the ketones-responsive active area by at least about 100mV.

Element 3: wherein the glucose-responsive active area comprises a firstelectron transfer agent covalently bonded to a polymer in the firstactive area and the ketones-responsive active area comprises a secondelectron transfer agent covalently bonded to a polymer in the secondactive area, the first and second electron transfer agents beingdifferent.

Element 4: wherein the glucose-responsive enzyme is covalently bonded tothe polymer in the glucose-responsive active area and one or more of theat least two enzymes in the enzyme system are covalently bonded to thepolymer in the ketones-responsive active area.

Element 5: wherein the analyte sensor further comprises a mass transportlimiting membrane overcoating the glucose-responsive active area and theketones-responsive active area.

Element 6: wherein the fluid is a biological fluid and the analytesensor is exposed to the biological fluid in vivo.

Element 7: wherein a mass transport limiting membrane overcoats theglucose-responsive active area and the ketones-responsive active area.

Element 8: wherein the first membrane is a multi-component membraneovercoating the ketones-responsive active area, the multi-componentmembrane comprising at least a first membrane polymer and a secondmembrane polymer that differ from one another, and the second membraneis a homogeneous membrane overcoating the glucose-responsive active areaand differing in composition from the multi-component membrane, thehomogeneous membrane comprising one of the first membrane polymer andthe second membrane polymer.

Element 9: wherein the multi-component membrane comprises a bilayermembrane.

Element 10: wherein the first membrane polymer is disposed directly uponthe ketones-responsive active area, the second membrane polymer isdisposed upon the first membrane polymer to define the bilayer membrane,and the homogenous membrane comprises the second membrane polymer.

Element 11: wherein the multi-component membrane comprises an admixtureof the first membrane polymer and the second membrane polymer.

Element 12: wherein the multi-component membrane comprisespolyvinylpyridine and polyvinylpyridine-co-styrene, and the homogeneousmembrane comprises polyvinylpyridine-co-styrene.

Element 13: wherein the glucose-responsive active area and theketones-responsive active area each comprise an electron-transfer agentthat is covalently bonded to a polymer in each of the glucose-responsiveactive area and the ketones-responsive active area.

Element 14: wherein the first signal and the second signal are measuredat different times.

Element 15: wherein the first signal and the second signal are obtainedsimultaneously via a first channel and a second channel.

By way of non-limiting example, exemplary combinations applicable to Aand B include: 1 and 2; 1 and 3; 1 and 4; 1 and 5; 2 and 3; 2 and 4; 2and 5; 3 and 4; 3 and 5; 4 and 5; 1 and 6; 2 and 6; 3 and 6; 4 and 6;and 5 and 6.

By way of further non-limiting example, exemplary combinationsapplicable to C and D include: 1 and 8; 4 and 8; 1 and 9; 4 and 9; 1 and10; 4 and 10; 1 and 11; 4 and 11; 1 and 12; 4 and 12; 1 and 13; 4 and13; 1 and 14; 4 and 14; 1 and 15; 4 and 15; 4 and 9; 4, 9 and 10; 4 and11; 4 and 12; 4 and 13; 4 and 14; 4 and 15; 8 and 9; 8-10; 8 and 11; 8and 12; 8 and 13; 8 and 14; 8 and 15; 9 and 10; 9 and 11; 9 and 12; 9and 13; 9 and 14; 9 and 15; 11 and 12; 11 and 13; 11 and 14; 11 and 15;12 and 13; 12 and 14; 12 and 15; 13 and 14; 13 and 15; and 14 and 15.

Additional embodiments disclosed herein include:

A′. Analyte sensors responsive to glucose and ketones. The analytesensors comprise: a sensor tail comprising at least a first workingelectrode and a second working electrode; a ketones-responsive activearea disposed upon a surface of the first working electrode, theketones-responsive active area comprising an enzyme system comprising atleast two enzymes that are capable of acting in concert to facilitatedetection of ketones; a glucose-responsive active area comprising aglucose-responsive enzyme disposed upon a surface of the second workingelectrode; and a membrane having a first portion overcoating theketones-responsive active area and a second portion overcoating theglucose-responsive active area; wherein the first portion and the secondportion have different compositions.

B′. Methods for assaying glucose and ketones using a single analytesensor. The methods comprise: exposing an analyte sensor to a fluidcomprising at least one of glucose and ketones; wherein the analytesensor comprises a sensor tail comprising at least a first workingelectrode and second working electrode, a ketones-responsive active areadisposed upon a surface of the first working electrode, aglucose-responsive active area disposed upon a surface of the secondworking electrode, and a membrane having a first portion overcoating theketones-responsive active area and a second portion overcoating theglucose-responsive active area; wherein the first portion and the secondportion have different compositions; wherein the glucose-responsiveactive area comprises a glucose-responsive enzyme, and theketones-responsive active area comprises an enzyme system comprising atleast two enzymes that are capable of acting in concert to facilitatedetection of ketones; applying a potential to the first workingelectrode and the second working electrode; obtaining a first signal ator above an oxidation-reduction potential of the glucose-responsiveactive area, the first signal being proportional to a concentration ofglucose in the fluid; obtaining a second signal at or above anoxidation-reduction potential of the ketones-responsive active area, thesecond signal being proportional to a concentration of ketones in thefluid; and correlating the first signal to the concentration of glucosein the fluid and the second signal to the concentration of ketones inthe fluid.

Element 1′: wherein the first portion is multi-component and comprisesat least a first membrane polymer and a second membrane polymer thatdiffer from one another.

Element 2′: wherein the second portion is homogenous and comprises oneof the first membrane polymer and the second membrane polymer.

Element 3′: wherein the first portion comprises at least two membranelayers.

Element 4′: wherein the first membrane polymer is disposed directly uponthe ketones-responsive active area, and the second membrane polymer isdisposed upon the first membrane polymer and upon the glucose-responsiveactive area.

Element 5′: wherein the first portion of the membrane is thicker thanthe second portion of the membrane.

Element 6′: wherein the first portion of the membrane comprisespolyvinylpyridine and polyvinylpyridine-co-styrene, and the secondportion of the membrane comprises polyvinylpyridine-co-styrene.

Element 7′: wherein the first portion of the membrane comprises anadmixture of the first membrane polymer and the second membrane polymer.

Element 8′: wherein the first portion and the second portion define acontinuous membrane overcoating the ketones-responsive active area andthe glucose-responsive active area.

Element 9′: wherein the sensor tail is configured for insertion into atissue.

Element 10′: wherein the glucose-responsive active area and theketones-responsive active area each comprise an electron-transfer agentthat is covalently bonded to a polymer in each of the glucose-responsiveactive area and the ketones-responsive active area.

Element 11′: wherein the glucose-responsive enzyme is covalently bondedto the polymer in the glucose-responsive active area and one or more ofthe at least two enzymes in the enzyme system are covalently bonded tothe polymer in the ketones-responsive active area.

Element 12′: wherein the fluid is a biological fluid and the analytesensor is exposed to the biological fluid in vivo.

Element 13′: wherein the first signal and the second signal are measuredat different times.

Element 14′: wherein the first signal and the second signal are obtainedsimultaneously via a first channel and a second channel.

By way of non-limiting example, exemplary combinations applicable to A′and B′ include: 1′ and 2′; 1′ and 3′; 1′, 3′ and 4′; 1′-4′; 1′ and 5′;1′ and 6′; 1′ and 7′; 1′ and 8′; 1′ and 9′; 1′ and 10′; 1′ and 11′; 2′and 3′; 3′ and 4′; 2′-4′; 3′ and 5′; 3′ and 6′; 3′ and 7′; 3′ and 8′; 3′and 9′; 3′ and 10′; 3′ and 11′; 3′-5′; 3′, 4′ and 6′; 3′ and 4′; 3′, 4′and 8′; 3′, 4′ and 9′; 3′, 4′ and 10′; 3′, 4′ and 11′; 6′ and 7′; 7′ and8′; 7′ and 9′; 7′ and 10′; 7′ and 11′; 8′ and 9′; 8′ and 10′; 8′ and11′; 10′ and 11′, any of which may be in further combination withelement 12′; element 13′ or element 14′. Other exemplary combinationsapplicable to B′ include any one of elements 1′-11′ in combination withone or more of element 12′, element 13′ or element 14′; 12′ and 13′; and12′ and 14′.

To facilitate a better understanding of the embodiments describedherein, the following examples of various representative embodiments aregiven. In no way should the following examples be read to limit, or todefine, the scope of the invention.

Examples

A poly(vinylpyridine)-bound transition metal complex having thestructure shown in Formula 1 was prepared. Further details concerningthis transition metal complex and electron transfer therewith isprovided in commonly owned U.S. Pat. No. 6,605,200, which wasincorporated by reference above. The subscripts for each monomerrepresent illustrative atomic ratios and are not indicative of anyparticular monomer ordering.

Example 1: Detection of Ketones Using an Analyte Sensor HavingDiaphorase and β-Hydroxybutyrate Dehydrogenase Acting in Concert. Forthis example, the enzyme system of FIG. 2A was used to facilitatedetection of ketones. The spotting formulation shown in Table 1 belowwas coated onto a carbon working electrode. Deposition was performed toplace six spots, each having an area of around 0.01 mm², upon theworking electrode. Following deposition, the working electrode was curedovernight at 25° C. Thereafter, a homogeneous PVP membrane was appliedto the working electrode via dip coating using a coating solutionformulated with 4 mL of 100 mg/mL PVP, 0.2 mL of 100 mg/mL PEGDGE400(PEGDGE with a molecular weight of approximately 400), and 0.0132 mL of100 mg/mL polydimethylsiloxane (PDMS). Membrane curing was performed for24 hours at 25° C., followed by 48 hours at 56° C. in desiccated vials.

TABLE 1 β-Hydroxybutyrate Dehydrogenase (HBDH) in 10 mM MES Buffer at pH= 5.5 Concentration Component (mg/mL) HBDH 8 Diaphorase 4 Albumin 8 NAD⁺8 Formula 1 8 Polymer PEGDGE400 4

Ketone analyses were conducted by immersing the electrode in 100 mM PBSbuffer (pH=7.4) at 33° C. and introducing various amounts ofβ-hydroxybutyrate (0, 1, 2, 3, 4, 6 and 8 mM total β-hydroxybutyrateaddition) as a ketones surrogate. FIG. 6 shows four replicates of theresponse for an electrode containing diaphorase, NAD⁺, andβ-hydroxybutyrate dehydrogenase when exposed to varyingβ-hydroxybutyrate concentrations. Only two traces are apparent in FIG. 6due to overlap of the signal response for the four sensors tested. Asshown, the current response increased over the course of several minutesfollowing exposure to a new β-hydroxybutyrate concentration beforestabilizing thereafter. FIG. 7 shows an illustrative plot of averagecurrent response versus β-hydroxybutyrate concentration for theelectrodes of FIG. 6 . The ketone sensors also exhibited a stableresponse over extended measurement times, as shown in FIG. 8 . FIG. 8shows an illustrative plot of current response for the electrodes ofFIG. 6 when exposed to 8 mM of β-hydroxybutyrate in 100 mM PBS at 33° C.for 2 weeks. The mean signal loss over the measurement period was only3.1%.

Example 2: Detection of Glucose and Ketones Using an Analyte SensorHaving a Glucose-Responsive Active Area and a Ketones-Responsive ActiveArea on Separate Working Electrodes. For this example, an analyte sensorwas prepared with a glucose-responsive active area comprising glucoseoxidase deposited upon a first working electrode and aketones-responsive active area comprising diaphorase andβ-hydroxybutyrate dehydrogenase deposited upon a second workingelectrode. The two working electrodes were carbon electrodes disposedupon opposing faces of a planar dielectric substrate.

The glucose-responsive active area was deposited upon the first workingelectrode using the glucose oxidase formulation specified in Table 2below. Active area deposition was conducted by placing five discrete,separate spots, each having an area of approximately 0.01 mm², upon theworking electrode. Following deposition, the working electrode was curedovernight at 25° C.

TABLE 2 Glucose Oxidase (GOX) Formulation in 10 mM HEPES Buffer at pH =8 Initial Added Final Concentration Volume Concentration Component(mg/mL) (mL) (mg/mL) GOX 60 0.41 24.6 Formula 1 60 0.34 20.4 PolymerPEGDE400 60 0.25 15

The ketones-responsive active area was deposited upon the second workingelectrode using the diaphorase/β-hydroxybutyrate formulation specifiedin Table 1 above. Active area deposition and curing was conducted as inExample 1 above, except five sensing spots were deposited in thisinstance. Curing of the ketones-responsive active area and theglucose-responsive active area was conducted at the same time.

Following deposition of the active areas, a bilayer membrane wasdeposited upon the ketones-responsive active area as follows. A PVPmembrane was first deposited upon the ketones-responsive active areausing via a modified slot coating procedure. The PVP membrane in thisexample was deposited from a coating solution formulated with 4 mL of160 mg/mL PVP, 0.133 mL of 100 mg/mL PEGDGE400, and 0.0132 mL of 100mg/mL PDMS. Curing was then performed for 24 hours at 25° C. The slotcoating procedure was conducted using a syringe pump to pump the coatingsolution from a nozzle located a small distance above a row of sensortails. The coating solution was pumped at a constant rate while movingthe nozzle at a fixed rate across the row of sensor tails. Parameterssuch as flow rates, nozzle diameter, the rate of nozzle movement, thedistance between the nozzle and the sensor tails, the solutionviscosity, the temperature, and the solvent were varied to afford amembrane having a desired thickness.

Thereafter, the entire assembly (i.e., both working electrodes, theglucose-responsive active area, the PVP coating upon the workingelectrode containing the ketones-responsive active area, and the counterand reference electrodes) was dip coated to introduce a crosslinkedpolyvinylpyridine-co-styrene membrane polymer thereon. The membranepolymer coating the entire assembly was deposited using 4 mL ofpolyvinylpyridine-co-styrene in 80:20 ethanol:HEPES buffer (140 mg/mL),0.2 mL PEGDGE400 in 80:20 ethanol:HEPES buffer (100 mg/mL), and 0.0132mL of aminopropyl-terminated polydimethylsiloxane (PDMS) in ethanol (100mg/mL). Curing was again performed for 24 hours at 25° C., followed by48 hours at 56° C. in a desiccated environment. Thus, a homogeneousmembrane (polyvinylpyridine-co-styrene) was deposited upon theglucose-responsive active area and a bilayer membrane (inner layer ofPVP and outer layer of polyvinylpyridine-co-styrene) was deposited uponthe ketones-responsive active area.

The analyte sensor was used to assay for glucose and ketonessimultaneously in 100 mM PBS at 37° C. In a first experiment, the sensorwas exposed for 2 weeks at 37° C. to a 100 mM PBS solution containing 30mM glucose and 10 mM β-hydroxybutyrate (ketones surrogate). The sensorwas held at +40 mV relative to Ag/AgCl for this experiment. FIG. 9 showsan illustrative plot of the response for an analyte sensor containing aglucose-responsive active area and a ketones-responsive active areadisposed upon separate working electrodes following exposure to 30 mMglucose and 10 mM ketones. As shown, the response of the analyte sensorremained very steady over the observation period for both analytes.

Next, glucose and β-hydroxybutyrate were added incrementally to 100 mMPBS at 37° C. to determine the response of the analyte sensor towardeach analyte. The sensor was again held at +40 mV relative to Ag/AgClfor this test. Glucose was added over a concentration range of 0-30 mM,and β-hydroxybutyrate was added over a concentration range of 0-10 mM.Each analyte was added simultaneously at concentrations of 10 mM orunder. Above 10 mM, only additional glucose was added to the solution,with 10 mM representing the maximum ketones concentration tested. FIGS.10-12 show illustrative plots of the analyte sensor response to varyingconcentrations of glucose and β-hydroxybutyrate. As shown in FIGS. 10and 11 , the analyte sensor afforded a linear response toward bothanalytes over the tested concentration ranges. As shown in FIG. 12 , thesensor response was rapid for both analytes and remained stable at agiven analyte concentration.

Example 3: Detection of Ketones Using an Analyte Sensor Having NADHOxidase and p-Hydroxybutyrate Dehydrogenase Acting in Concert. For thisexample, the enzyme system of FIG. 2B was used to facilitate detectionof ketones. The spotting formulation shown in Table 3 below was coatedonto either a carbon working electrode or a carbon nanotube workingelectrode. Coating was conducted by hand in 3 passes to coat theentirety of the sensor tip. The mean active area was 3.0 mm² for thecarbon working electrode and 7.6 mm² for the carbon nanotube workingelectrode. Following deposition, the working electrodes were curedovernight at 25° C. Thereafter, a PVP membrane was applied to theworking electrodes via dip coating using a coating solution formulatedwith 4 mL of 100 mg/mL PVP and 0.2 mL of 100 mg/mL PEGDGE400. Membranecuring was performed for 24 hours at 25° C.

TABLE 3 β-Hydroxybutyrate Dehydrogenase (HBDH) in 10 mM MES Buffer at pH= 5.5 Concentration Component (mg/mL) HBDH 8 Albumin 8 NAD⁺ 8 NADHOx 8PVI 8 PEGDGE400 4

Ketone analyses were conducted as set forth in Example 1. FIGS. 13A and13B show four replicates of the response for an electrode containingNADHOx, NAD⁺, and β-hydroxybutyrate dehydrogenase when exposed tovarying p-hydroxybutyrate concentrations. FIG. 13A shows the currentresponse for a carbon working electrode, and FIG. 13B shows the currentresponse for a carbon nanotube working electrode. As shown, the currentresponse for both types of working electrode increased as theβ-hydroxybutyrate concentration increased up to a concentration of 10mM. FIG. 14 shows an illustrative plot of current response versus timefor an electrode containing NADHOx, NAD⁺, and β-hydroxybutyratedehydrogenase after exposure to increasing β-hydroxybutyratedehydrogenase concentrations. As shown, the current increased rapidlyafter adding β-hydroxybutyrate dehydrogenase and stabilized thereafter.

Example 4: Detection of Ketones Using an Analyte Sensor ContainingPoly-1,10-phenanthroline-5,6-dione and p-Hydroxybutyrate Dehydrogenase.For this example, the enzyme system of FIG. 2C was used to facilitatedetection of ketones. The spotting formulation shown in Table 4 belowwas coated onto either a carbon working electrode or a carbon nanotubeworking electrode. Coating and curing of the spotting formulation andthe PVP membrane was conducted as specified in Example 3. The meanactive area was 3.0 mm² for the carbon working electrode and 7.6 mm² forthe carbon nanotube working electrode.

TABLE 4 β-Hydroxybutyrate Dehydrogenase (HBDH) in 10 mM MES Buffer at pH= 5.5 Concentration Component (mg/mL) HBDH 8 Albumin 8 NAD⁺ 81,10-phenanthroline-5,6-dione 8 PVI 8 PEGDGE400 4

Ketone analyses were conducted as set forth in Example 1. FIGS. 15A and15B show four replicates of the response for an electrode containingpoly-1,10-phenanthroline-5,6-dione and β-hydroxybutyrate dehydrogenasewhen exposed to varying β-hydroxybutyrate concentrations. FIG. 15A showsthe current response for a carbon working electrode, and FIG. 15B showsthe current response for a carbon nanotube working electrode. As shown,the current response for both types of working electrode increased asthe β-hydroxybutyrate concentration increased up to a concentration ofabout 2 mM before the response began to flatten.

Analyte Sensor Ignition Lock

Vehicle fail safes, such as ignition locks, are sometimes used toprevent an operator from operating a vehicle when impaired or otherwisenot in a condition to safely operate the vehicle. Operating the vehiclewhile impaired could potentially present significant dangers to theoperator and the public. One common type of ignition lock is designed toprevent drunk driving and, more specifically, to prevent individualsfrom operating a vehicle while intoxicated through alcohol use. Suchlock devices connect a breath-alcohol analyzer or optical sensor to thevehicle's ignition system, and the driver must successfully pass a bloodalcohol level test before the vehicle can be started.

Intoxication is one type of impairment or condition that an operator mayexperience that renders the operator unfit or unable to operate avehicle. However, other impairments and conditions can also afflict anoperator and should also be monitored closely to ensure the operatordoes not operate a vehicle while impaired. For example, an operator withdiabetes and driving while hypoglycemic (i.e., low blood sugar) couldpotentially undergo light-headedness, confusion, headache, loss ofconsciousness, seizures, and delayed reflexes, any of which couldendanger his/her own life and those in the vehicle or in the vicinity ofthe vehicle.

Analyte monitoring systems, have been developed to facilitate long-termmonitoring of analytes in bodily fluid (e.g., blood). Some analytemonitoring systems are designed to detect and monitor levels of bloodglucose, which can be helpful in treating diabetic conditions. Otheranalyte monitoring systems, however, are designed to detect and monitorother analytes present in an operator's bodily fluid, and abnormalanalyte levels detected in an operator may be indicative that theoperator is currently unfit to safely operate a vehicle.

The following discussion describes an analyte monitoring and vehiclecontrol system used to prevent operation of a vehicle when operatoranalyte levels cross a predetermined threshold. Having the sensorcontrol device 102 (FIG. 1 ) properly deployed allows a user tointelligently track and monitor bodily fluid analyte levels and trends.When some analyte levels surpass certain thresholds, physical orcognitive impairment may ensue that renders a user unfit to safelyoperate a vehicle. In such instances, the user should take appropriateaction to bring analyte levels back into safe ranges prior to attemptingto operate a vehicle. In some cases, however, a user may feel perfectlyfine to operate a vehicle but nonetheless have unsafe analyte levelsthat could suddenly trigger the onset of a dangerous physicalimpairment. In such cases, it may be advantageous to have a failsafesystem in place that prevents or warns the user from operating a vehicleand potentially placing self and/or others in danger.

FIG. 16 is a schematic diagram of an example analyte monitoring andvehicle control system 1600, according to one or more embodiments of thepresent disclosure. As illustrated, the analyte monitoring and vehiclecontrol system 1600 (hereafter “the system 1600) includes the sensorcontrol device 102, which may be deployed on a user or “operator” 3202and otherwise delivered to a target monitoring location on the body ofthe operator 1602, such as the back of an arm. As discussed above, thesensor control device 102 includes the sensor 104 (FIG. 1 ), and whenproperly deployed, the sensor 104 is positioned transcutaneously withinthe skin to detect and monitor analytes present within a bodily fluid ofthe operator 1602. The adhesive patch 105 (FIG. 1 ) applied to thebottom of the sensor control device 102 adheres to the skin to securethe sensor control device 102 in place during operation.

While the system 1600 is described herein as including the on-bodysensor control device 102 to detect and report analyte levels, thesystem 1600 may alternatively incorporate an ex vivo analyte sensor(e.g., a self-monitoring blood glucose “SMBG” meter), without departingfrom the scope of the disclosure. Accordingly, the term “sensor controldevice” should be interpreted herein to include not only on-body sensorsystems, as generally described above, but also traditional, hand-heldsensor systems.

As illustrated, the system 1600 may further include the reader device120, and the sensor control device 102 may be in communication with thereader device 120 via a local communication path or link to provideanalyte concentration data automatically, periodically, or as desired bythe operator 1602. The reader device 120 may be in communication with acontrol module 1604, which is in communication with the electricalsystem of a vehicle 1606 and powered by the vehicle battery or otherwisepowered by a separate battery. In such embodiments, data transmitted tothe reader device 120 from the sensor control device 102 may besubsequently transmitted by the reader device 120 to the control module1604 for processing. In other embodiments, however, the sensor controldevice 102 may communicate directly with the control module 1604 via anywireless communication protocol, such as BLUETOOTH®. In suchembodiments, the reader device 120 may or may not be necessary in thesystem 1600.

In the illustrated embodiment, the vehicle 1606 is depicted as anautomobile. As used herein, however, the term “vehicle” is used broadlyand is meant to include any kind of transportation vehicle that can beoperated by a human user or “operator,” but can also include autonomousvehicles used to transport humans. Examples of the vehicle 1606 include,but are not limited to, any type of automobile, truck, sport utilityvehicle, aircraft, watercraft, spacecraft, and or any other means oftransportation, or combinations thereof.

The control module 1604 may include a communications interface tocommunicate information to/from the sensor control device 102 and/or thereader device 120. In the case of an exemplary BLUETOOTH®-enabled sensorcontrol device 102 and/or reader device 120, a pairing mode may beentered into when the sensor control device 102 approaches the vehicle1606. Upon pairing, the control module 1604 may be programmed andconfigured to automatically detect the presence of and establishcommunication with the sensor control device 102 and/or the readerdevice 120. For example, when the operator 1602 approaches or enters thevehicle 1606, the control module 1604 may automatically detect thepresence of the sensor control device 102 and enable communicationtherebetween or with the reader device 120.

In some embodiments, the control module 1604 may be in communicationwith a vehicle user interface 1608 included in the vehicle 1606, such asan infotainment system, a touchscreen display, or an informationdisplay. In such embodiments, the control module 1604 may visuallycommunicate with the operator 1602 via the vehicle user interface 1608and may also be able to audibly communicate with the operator 1602 viathe audio speakers included in the vehicle 1606. In other embodiments,however, the control module 1604 may be configured to communicate withthe reader device 120 to be able to communicate with the operator 1602.

As illustrated, the control module 1604 may be or otherwise include acomputer system 1610 configured and otherwise programmed to controlvarious operations and/or systems of the vehicle 1606 based on real-timemeasured analyte levels of the operator 1602 as obtained by the sensorcontrol device 102. Operation of the vehicle 1606 is controlled,disabled, or modified by either disabling one or more critical systemsof the vehicle 1606 or by activating warning systems in the vehicle1606. When the real-time measured analyte levels of the operator 1602are within a predetermined safe range, then it may be considered safefor the operator 1602 to operate the vehicle 1606. When the real-timemeasured analyte levels of the operator 1602 fall outside thepredetermined safe range or cross a predetermined threshold, however,the computer system 1610 may then be programmed to control, disable, ormodify operation of the vehicle 1606.

In some embodiments, for example, the computer system 1610 may beconfigured to disable various critical vehicle systems when detectedanalyte levels of the operator 1602 fall outside of a predeterminedrange or otherwise cross a predetermined threshold, thus progressivelyand safely disabling operation of the vehicle when identifying theoperator 1602 as impaired for safe operation of the vehicle 1606.Critical vehicle systems of the vehicle 1606 that may be disabledinclude the ignition system (e.g., energy switching/control system), thetransmission system (or gear box), the fuel system, energy supply system(e.g., a battery, capacitor, conversion/reaction cell, etc.). Whenelevated or lowered (unsafe) analyte levels are detected, the computersystem 1610 may prevent the critical vehicle systems from functioning oroperating. Consequently, the operator 1602 will be unable to start oroperate the vehicle 1606, thereby preventing the operator 1602 fromplacing themselves and/or others in danger.

In other embodiments, or in addition thereto, the computer system 1610may be configured to activate various non-critical vehicle systems whendetected analyte levels of the operator 1602 surpass or cross apredetermined threshold. Non-critical vehicle systems that may beactivated include, for example, the vehicle horn, the vehicle lights, oran audible warning system installed in the vehicle 1606. In suchembodiments, activation of the non-critical vehicle systems may alertlaw enforcement and others (e.g., operators of adjacent vehicles,bystanders, pedestrians, etc.) of an operator 1602 that may be drivingin an impaired condition, thus allowing law enforcement to quicklyaddress any issues related thereto and placing others on notice of apotentially dangerous situation.

In yet other embodiments, or in addition thereto, the computer system1610 may be configured to automatically place a phone call to one ormore emergency contacts when analyte levels of the operator 1602 falloutside of a predetermined safe operating range or otherwise cross apredetermined threshold. In such embodiments, the computer system 1610may operate through the reader device 120 (e.g., a cellular phone) or acellular or satellite communication system incorporated into the vehicle1606 (e.g., OnStar®). In other embodiments, or in addition thereto, thecomputer system 1610 may be configured to automatically send a message(e.g., text or SMS message, email, etc.) to an emergency contact whenanalyte levels of the operator 1602 fall outside of a predetermined safeoperating range or otherwise cross a predetermined threshold. Exampleemergency contacts include, but are not limited to, a spouse, a parent,medical personnel (e.g., a doctor), a hospital, 911, or any combinationthereof.

In some embodiments, the system 1600 may further include one or moreproximity sensors 1612 configured to detect the presence of the operator1602 and, more particularly, the sensor control device 102. In suchembodiments, the proximity sensor(s) 1612 may be configured to monitorthe general area of the driver's seat 1614 within the vehicle 1606. Ifthe sensor control device 102 is detected within the area of thedriver's seat 1614 by the proximity sensor(s) 1612, that may provide apositive indication that the operator 1602 is in the driver's seat 1614and potentially attempting to operate the vehicle 1606. In such cases, asignal may be sent to the control module 1604 alerting the computersystem 1610 that the operator 1602 is in the vehicle 1606 andpotentially attempting to operate the vehicle 1606. If the real-timemeasured analyte levels of the operator 1602 are within a predeterminedsafe range or below a predetermined level, then the computer system 1610may allow the operator 1602 to operate the vehicle 1606. When thereal-time measured analyte levels of the operator 1602 fall outside thepredetermined safe range or cross a predetermined threshold, however,the computer system 1610 may control, disable, or modify operation ofthe vehicle 1606, as generally described above. As will be appreciated,the proximity sensor(s) 1612 may be advantageous in preventing operationof the vehicle 1606 only when the impaired operator 1602 is in thedriver's seat 1614 and ready to operate the vehicle 1606. Consequently,a user wearing the sensor control device 102 is able to ride as apassenger in the vehicle 1606 in any state without affecting operationof the control module 1604 or the vehicle 1606.

In some embodiments, the control module 1604 may further include avehicle status detection module 1616 configured to detect the currentstatus of the vehicle 1606, including whether the vehicle 1606 iscurrently moving or is stationary. In addition, the vehicle statusdetection module 1616 may be configured to determine whether or not themotor in the vehicle 1606 is currently operating or is stopped. In oneor more embodiments, the vehicle status detection module 1616 mayprovide a status signal to the control module 1604, and the controlmodule 1604 can then use the status signal to determine what vehicleoperations should be activated or disabled when the real-time measuredanalyte levels of the operator 1602 fall outside the predetermined saferange or cross a predetermined threshold. For example, when the statussignal indicates that the vehicle 1606 is stationary, the control module1604 can disable the vehicle fuel system, transmission system, ignitionsystem, or any combination thereof. In contrast, when the status signalindicates that the vehicle 1606 is moving, the control module 1604 canactivate the vehicle horn, flash the vehicle lights, or activate anaudible warning to the operator 1602 and/or those around the operator1602 that the operator 1602 is impaired.

In some embodiments, once the operator 1602 enters the vehicle 1606 orwhen the control module 1604 pairs with the sensor control device 102and/or the reader device 120, an app may be launched on the readerdevice 120 or the vehicle user interface 1608, and a digital dashboardmay appear on the reader device 120 and/or the vehicle user interface1608 that depicts current analyte levels, trend, historical data, andprojected analyte levels. If the current analyte levels fall outside ofa predetermined safe operating range, however, the computer system 1610may be programmed to disable one or more critical vehicle systems toprevent the operator 1602 from operating the vehicle 1606. In suchembodiments, a visual or audible alert may be issued by the controlmodule 1604 to inform the operator 1602 as to why the vehicle 1606 isnot starting. More particularly, a visual alert (e.g., a writtenmessage) may be generated and displayed on the reader device 120 or thevehicle user interface 1608, or an audible alert (e.g., a vocal message)may be transmitted through the speakers in the reader device 120 or thevehicle 1606.

If not done automatically, the operator 1602 may be prompted to obtain acurrent analyte level upon pairing the sensor control device 102 withthe control module 1604. In some cases, the vehicle 1606 may beprevented from being operated until a current analyte level is obtained.If the current analyte levels are within safe limits, the computersystem 1610 may allow operation of the vehicle 1606. In some aspects,and unless done automatically, the control module 1604 may prompt theoperator 1602 to obtain additional current analyte levels afteroperating the vehicle 1606 for a predetermined period of time (e.g.,after 1 hour, 2 hours, 5 hours, etc.).

In some embodiments, the control module 1604 may be configured to issuevisual or audible recommendations or coaching to the operator 1602 thatmay help bring measured analyte levels back into safe ranges. In suchembodiments, such visual or audible recommendations may prompt the userto take some action that could result in bringing analyte levels backinto safe ranges. Moreover, in some embodiments, the operator 1602 maybe able to communicate with the control module 1604 verbally by issuingverbal responses or commands. This may prove advantageous in helpingprevent distracted operation of the vehicle 1606.

In some embodiments, settings of the control module 1604 may becustomized by the operator 1602 to allow the user to make informeddecisions once unsafe analyte levels have been detected and a visual oraudible alert has been issued by the control module 1604. Morespecifically, in at least one embodiment, the control module 1604 mayinclude a bypass feature that the operator 1602 might enable to allowthe operator 1602 to operate the vehicle 1606 even when unsafe analytelevels have been measured. In such embodiments, the operator 1602 mayoperate the vehicle 1606 by acknowledging that the operator 1602 mightbe operating the vehicle 1606 in an impaired or unsafe health state.

In some embodiments, the computer system 1610 may be configured orotherwise programmed to calculate a predicted timeline when analytelevels of the operator 1602 may depart from a predetermined safe rangeor otherwise cross a predetermined threshold. In such embodiments, thecontrol module 1604 may be configured to issue visual or audible alertsto the operator 1602 indicating approximately how much time the operator1602 has before unsafe analyte levels may be reached and a potentialunsafe medical condition may ensue. Multiple alerts may be provided toindicate when the operator has specific time increments remaining beforeunsafe analyte levels are reached. For example, visual or audible alertsmay be issued when unsafe analyte levels will be reached within an hour,within a half hour, within 10 minutes, within 5 minutes, within 1minute, and any time increment therebetween. Furthermore, a visual oraudible alert may be issued once the analyte levels of the operatorreach an unsafe level or cross a predetermined threshold.

In some embodiments, if unsafe analyte levels are measured while theoperator 1602 is operating the vehicle 1606, the control module 1604 maybe configured to issue one or more alerts (visual or audible) warningthe operator 1602 of the unsafe analyte levels. In some cases, thevolume of the stereo in the vehicle 1606 may be automatically lowered toenable the operator 1602 to hear an audible alert. In such embodiments,the control module 1604 may be configured to suggest one or morecorrective actions to the operator 1602. Example corrective actionsinclude, but are not limited to, slowing and stopping the vehicle 1606,locating and driving to a nearby convenience store or pharmacy, andlocating a nearby hospital or medical facility. If the vehicle 1606 isan autonomous vehicle, and the current analyte levels place the operator1602 in potentially dangerous conditions, the control module 1604 mayautomatically direct the vehicle 1606 to a medical facility fortreatment. Alternatively, or in addition thereto, the control module1604 may progressively reduce or restrict the speed of the vehicle 1606when unsafe analyte levels are detected, thus forcing the operator 1602to come to a stop and remedy the issue before continuing to operate thevehicle 1606.

The system 1600 may be useful in several different scenarios to protectthe operator 1602 and/or those around the operator 1602 while driving.In some applications, the system 1600 may be incorporated voluntarily bythe operator to detect impairment in real-time. In other applications,the system 1600 may be required by the owner of the vehicle 1606 todetect impairment of the operator 1602. In such applications, the ownerof the vehicle 1606 may be a transport or trucking company. In yet otherapplications, the system 1600 may be legally imposed on the operator1602 to detect impairment.

Embodiments disclosed herein include:

E. An analyte monitoring and vehicle control system that includes asensor control device having a sensor that detects and monitors one ormore analytes present within a body of an operator, and a control modulein communication with the sensor control device and an electrical systemof a vehicle, the control module including a computer system programmedto receive and process data provided by the sensor control device,wherein operation of the vehicle is controlled or disabled by thecomputer system when a real-time measured analyte level of the operatorcrosses a predetermined safe threshold.

F. A method that includes detecting and monitoring one or more analytespresent within a body of an operator with a sensor control device havinga sensor, receiving and processes data provided by the sensor controldevice with a control module in communication with the sensor controldevice and an electrical system of a vehicle; and controlling ordisabling operation of the vehicle with a computer system of the controlmodule when a real-time measured analyte level of the operator crosses apredetermined safe threshold.

Each of embodiments E and F may have one or more of the followingadditional elements in any combination: Element 1: wherein the sensorcontrol device is coupled to the operator and the sensor istranscutaneously positioned beneath skin of the operator to detect andmonitor the analytes present within a bodily fluid of the operator.Element 2: wherein the sensor control device comprises an ex vivoanalyte sensor. Element 3: further comprising a reader device thatreceives the data from the sensor control device and transmits the datato the control module. Element 4: wherein the vehicle comprises atransportation vehicle selected from the group consisting of anautomobile, an autonomous vehicle, a truck, a sport utility vehicle, anaircraft, a watercraft, a spacecraft, or any combination thereof.Element 5: wherein sensor control device pairs with the control modulefor communication upon the operator approaching the vehicle. Element 6:further comprising a vehicle user interface included in the vehicle andin communication with the control module. Element 7: wherein operationof the vehicle is disabled by disabling one or more critical systems ofthe vehicle, the critical systems being selected from the groupconsisting of an ignition system, a transmission system, a fuel system,and an energy supply system. Element 8: wherein operation of the vehicleis controlled by at least one of activating one or more non-criticalsystems of the vehicle, calling or sending a message to one or moreemergency contacts, and progressively reducing a speed of the vehicle.Element 9: further comprising one or more proximity sensors installed onthe vehicle to monitor an area of a driver's seat of the vehicle anddetect a presence of the operator. Element 10: wherein the controlmodule further includes a vehicle status detection module that detectsthe current status of the vehicle. Element 11: wherein the controlmodule generates visual or audible alerts perceivable by the operatorwhen the real-time measured analyte level of the operator falls outsideof the predetermined safe threshold. Element 12: wherein the visual oraudible alerts are generated at specific time increments before unsafeanalyte levels are reached. Element 13: wherein the visual or audiblealerts comprise one or more suggested corrective actions communicated tothe operator. Element 14: wherein the control module includes a bypassfeature allowing the operator to operate the vehicle when the real-timemeasured analyte level of the operator crosses the predeterminedthreshold.

Element 15: further comprising receiving the data from the sensorcontrol device and transmitting the data to the control module with areader device in communication with the sensor control device and thecontrol module. Element 16: wherein disabling operation of the vehiclecomprises disabling one or more critical systems of the vehicle, thecritical systems being selected from the group consisting of an ignitionsystem, a transmission system, a fuel system, and an energy supplysystem. Element 17: wherein controlling operation of the vehiclecomprises at least one of activating one or more non-critical systems ofthe vehicle, calling or sending a message to one or more emergencycontacts, and progressively reducing a speed of the vehicle. Element 18:further comprising monitoring an area of a driver's seat of the vehicleand detecting a presence of the operator with one or more proximitysensors installed on the vehicle. Element 19: further comprisingdetecting the current status of the vehicle with a vehicle statusdetection module included in the control module. Element 20: furthercomprising generating visual or audible alerts perceivable by theoperator with the control module when the real-time measured analytelevel of the operator crosses the predetermined threshold.

Unless otherwise indicated, all numbers expressing quantities and thelike in the present specification and associated claims are to beunderstood as being modified in all instances by the term “about.”Accordingly, unless indicated to the contrary, the numerical parametersset forth in the following specification and attached claims areapproximations that may vary depending upon the desired propertiessought to be obtained by the embodiments of the present invention. Atthe very least, and not as an attempt to limit the application of thedoctrine of equivalents to the scope of the claim, each numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques.

One or more illustrative embodiments incorporating various features arepresented herein. Not all features of a physical implementation aredescribed or shown in this application for the sake of clarity. It isunderstood that in the development of a physical embodimentincorporating the embodiments of the present invention, numerousimplementation-specific decisions must be made to achieve thedeveloper's goals, such as compliance with system-related,business-related, government-related and other constraints, which varyby implementation and from time to time. While a developer's effortsmight be time-consuming, such efforts would be, nevertheless, a routineundertaking for those of ordinary skill in the art and having benefit ofthis disclosure.

While various systems, tools and methods are described herein in termsof “comprising” various components or steps, the systems, tools andmethods can also “consist essentially of” or “consist of” the variouscomponents and steps.

As used herein, the phrase “at least one of” preceding a series ofitems, with the terms “and” or “or” to separate any of the items,modifies the list as a whole, rather than each member of the list (i.e.,each item). The phrase “at least one of” allows a meaning that includesat least one of any one of the items, and/or at least one of anycombination of the items, and/or at least one of each of the items. Byway of example, the phrases “at least one of A, B, and C” or “at leastone of A, B, or C” each refer to only A, only B, or only C; anycombination of A, B, and C; and/or at least one of each of A, B, and C.

Therefore, the disclosed systems, tools and methods are well adapted toattain the ends and advantages mentioned as well as those that areinherent therein. The particular embodiments disclosed above areillustrative only, as the teachings of the present disclosure may bemodified and practiced in different but equivalent manners apparent tothose skilled in the art having the benefit of the teachings herein.Furthermore, no limitations are intended to the details of constructionor design herein shown, other than as described in the claims below. Itis therefore evident that the particular illustrative embodimentsdisclosed above may be altered, combined, or modified and all suchvariations are considered within the scope of the present disclosure.The systems, tools and methods illustratively disclosed herein maysuitably be practiced in the absence of any element that is notspecifically disclosed herein and/or any optional element disclosedherein. While systems, tools and methods are described in terms of“comprising,” “containing,” or “including” various components or steps,the systems, tools and methods can also “consist essentially of” or“consist of” the various components and steps. All numbers and rangesdisclosed above may vary by some amount. Whenever a numerical range witha lower limit and an upper limit is disclosed, any number and anyincluded range falling within the range is specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Also, the terms in the claims have their plain, ordinary meaningunless otherwise explicitly and clearly defined by the patentee.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the elements that itintroduces. If there is any conflict in the usages of a word or term inthis specification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

What is claimed is:
 1. An analyte sensor comprising: a sensor tailcomprising at least a first working electrode and a second workingelectrode, the sensor tail configured for insertion into a tissue; aketones-responsive active area disposed upon a surface of the firstworking electrode, the ketones-responsive active area comprising a firstpolymer and an enzyme system comprising at least two enzymes thatfacilitate detection of ketones; and a glucose-responsive active areadisposed upon a surface of the second working electrode, theglucose-responsive active area comprising a second polymer and aglucose-responsive enzyme, wherein the glucose-responsive active areaproduces a first signal proportional to a concentration of glucose, andwherein the ketones-responsive active area produces a second signalproportional to a concentration of ketones.
 2. The analyte sensor ofclaim 1, wherein the first signal is produced independently of thesecond signal.
 3. The analyte sensor of claim 1, wherein theketones-responsive active area further comprises albumin.
 4. The analytesensor of claim 1, wherein the glucose-responsive enzyme is covalentlybonded to the second polymer.
 5. The analyte sensor of claim 1, whereinone or more of the at least two enzymes is covalently bonded to thefirst polymer.
 6. The analyte sensor of claim 1, wherein each of the atleast two enzymes is covalently bonded to the first polymer.
 7. Theanalyte sensor of claim 1, wherein the glucose-responsive active areafurther comprises an electron transfer agent.
 8. The analyte sensor ofclaim 7, wherein the electron transfer agent is covalently bonded to thesecond polymer.
 9. The analyte sensor of claim 1, wherein theketones-responsive active area further comprises an electron transferagent.
 10. The analyte sensor of claim 9, wherein the electron transferagent is covalently bonded to the first polymer.
 11. The analyte sensorof claim 1, wherein the glucose-responsive enzyme is glucose oxidase orglucose dehydrogenase.
 12. The analyte sensor of claim 1, wherein theenzyme system comprises β-hydroxybutyrate dehydrogenase and diaphorase.13. The analyte sensor of claim 1, wherein the enzyme system comprisesβ-hydroxybutyrate dehydrogenase and nicotinamide adenine dinucleotideoxidase.
 14. The analyte sensor of claim 1, further comprising a firstmembrane disposed directly upon the ketones-responsive active area. 15.The analyte sensor of claim 1, further comprising a second membranedisposed upon the first membrane and upon the glucose-responsive activearea.
 16. The analyte sensor of claim 14, wherein the first membranecomprises polyvinylpyridine.
 17. The analyte sensor of claim 15, whereinthe second membrane comprises polyvinylpyridine-co-styrene.
 18. Theanalyte sensor of claim 1, wherein the first polymer comprisespolyvinylpyridine, polyvinylimidazole, or a copolymer thereof.
 19. Theanalyte sensor of claim 1, wherein the second polymer comprisespolyvinylpyridine, polyvinylimidazole, or a copolymer thereof.